Comparing fast thinking and slow thinking: The relative benefits of interventions, individual differences, and inferential rules

Abstract

Research on judgment and decision making has suggested that the System 2 process of slow thinking can help people to improve their decision making by reducing well-established statistical decision biases (including base rate neglect, probability matching, and the conjunction fallacy). In a large pre-registered study with 1,706 participants and 23,292 unique observations, we compare the effects of individual differences and behavioral interventions to test the relative benefits of slow thinking on performance in canonical judgment and decision-making problems, compared to a control condition, a fast thinking condition, an incentive condition, and a condition that combines fast and slow thinking. We also draw on the rule-based reasoning literature to examine the benefits of having access to a simple form of the rule needed to solve a specific focal problem. Overall, we find equivocal evidence of a small benefit from slow thinking, evidence for a small benefit to accuracy incentives, and clear evidence of a larger cost from fast thinking. The difference in performance between fast-thinking and slow-thinking interventions is comparable to a one-scale point difference on the 4-point Cognitive Reflection Test (CRT). Inferential rules contribute unique explanatory power and interact with individual differences to support the idea that System 2 benefits from a combination of slower processes and knowledge appropriate to the problem.

1 Introduction

With the popularity of Daniel Kahneman’s 2011 best-selling book, Thinking, Fast and Slow, the prescription to slow down our thinking has become increasingly common in popular translations of judgment and decision making (JDM) research. For example, a 2016 Harvard Business Review article argues that “the essential lesson for competitive-strategy decision-makers is not so fast… take your time and don’t be so sure” (Chussil, 2016). Similarly, a 2017 Harvard Business Review article states that “reflective thinking improves decision making by grounding it in a more integrated and coherent world view than one can have by acting only in the moment” (Reeves, Torres & Hassan, 2017).

But is the exhortation to slow down in order to think smarter sound advice? There are at least two reasons to be cautious about this claim and why more study is needed. First, thinking more slowly can be helpful only if it increases the chances of thinking more soundly about a problem. If one does not have access to the necessary rule for solving the problem or recognize that the rule applies in the given situation, then thinking slower is unlikely to help (Kahneman, 2000). Second, much of the evidence that favors slow thinking has alternative interpretations that may not support a general prescription.

For example, one argument for slow thinking is that people who are dispositionally-inclined to be more reflective are better at avoiding common decision biases (Frederick, 2005; Oeschssler, Roider & Schmitz, 2009; Cokely & Kelley, 2009; Obrecht, Chapman & Gelman, 2009; Koehler & James, 2010). However, it would be a logical leap to conclude from an individual difference variable that less reflective people can debias themselves by slowing down, or even that more reflective individuals reach correct answers because they are reflective. It could be, for example, that a common factor such as education or temperament causes people to become both reflective and knowledgeable about the applicable rules. Alternatively, a growing body of evidence suggests that people may reach correct answers by having good intuitions, rather than by using deliberation to correct bad intuitions (Thompson, Pennycook, Trippas & Evans, 2018; Raoelison, Thompson & De Neys, 2020). Experiments are needed to tease apart the possible causal mechanisms. Although some work has been done, if the aim is to be able to advise laypeople on whether and how to change their thinking style, we will argue that the requisite experiments have previously not been conducted and published. We aim to contribute research that can help provide an answer.

We investigate our questions using canonical JDM problems built on clear statistical rules that are integral to answering the problem successfully. We include a broad range of statistical reasoning problems that cue incorrect responses. Importantly, these problems are not representative of many real-world situations, although some behavioral tendencies such as judging probability by representativeness (Kahneman & Tversky, 1973) are sufficiently general that they apply across contexts. As an example of what we mean by a statistical rule, consider the famous Linda problem (adapted from Tversky & Kahneman, 1983).

Linda is 31 years old, single, outspoken and very bright. She majored in philosophy. As a student, she was deeply concerned with issues of discrimination and social justice, and also participated in anti-nuclear demonstrations.

Rank these from most (=1) to least (=3) probable.

1. (1) Linda is a bank teller.

2. (2) Linda is active in the feminist movement.

3. (3) Linda is a bank teller and is active in the feminist movement.

Most people rank option 3 as more probable than option 1 despite the normative rule that the conjunction of two events can be no more probable than either of its constituent parts. Failure to recognize that option 1 is more probable is known as the conjunction fallacy. Why do people succumb to it? The standard explanation is that they apply the representativeness heuristic, which in this example entails substituting their perception of the similarity between Linda’s description and the stereotype of a bank teller for a probability, which would require more effort to work out (Kahneman, 2011). Among those who commit the fallacy, however, some may have access to the basic conjunction rule and others may not. For an example of the latter, if you ask people “which is more probable, (1) a staircase has five steps, (2) a staircase is carpeted, or (3) a staircase has five steps and is carpeted?” some people may rate statement 3 as more likely than 1 or 2 because they do not think in terms of conjunctions.

Slow thinking might help someone on the Linda problem who can access the conjunction rule, prompting them to check whether their similarity-based judgment is valid. However, for someone who does not have access to the rule, slow thinking might only lead them to more diligently and carefully apply faulty heuristic reasoning, as they lack access to the rule necessary to improve accuracy. Individuals’ likelihood of accessing and applying rules will vary significant across contexts and domains: Access to inferential rules is a matter of degree (Flavell, 1971). The two-question measure of each specific inferential rule we use in our experiment serves to measure whether participants had some minimal access to the relevant rule, without which it would be difficult to answer the harder JDM questions.

2 Literature review and theoretical development

There is a long tradition in research on judgment and decision making of examining the cognitive processes that lead individual judgments to deviate systematically from a normative standard. For nearly as long, the field has also considered how decision makers might be helped to make better decisions. Different research programs have proposed different approaches. In the 1980s, Nisbett and colleagues examined whether knowledge of simple rules could help people make better decisions (Nisbett & Ross, 1980; Kunda & Nisbett, 1986; Nisbett, Fong, Lehman & Cheng, 1987). From the 1990s to present day, dual process theories of decision making have argued for the benefits of slower, more deliberate thinking (System 2) as a means to make better decisions (Sloman, 1996; Stanovich & West, 1999, 2000; Kahneman & Frederick, 2002; Evans & Stanovich, 2013). Both rule-based and dual-process theories offer “internal” interventions that propose that individual cognitive processes can be improved – either by more ready access to rules of reasoning, or use of a different style of thinking. This contrasts with a more recent approach to nudge people toward better decisions through “external” situational interventions (Thaler & Sunstein, 2008).

In this paper, we build on the two internal approaches to examine the benefits of slowing down one’s thinking for individual decision making. Rule-based approaches to improving decision making focus on training people in abstract rules that apply across situations (Fong, Krantz & Nisbett, 1986; Morewedge et al., 2015). In contrast, dual process approaches focus on differences in cognitive processes, distinguishing rapid, automatic, and intuitive processes (System 1) from slower, analytic, and deliberative processes (System 2) (Kahneman, 2011; Sloman, 1996; Stanovich & West, 1999, 2000; Chaiken & Trope, 1999). The two systems are not fully distinct categories — Evans and Stanovich (2013) have encouraged a movement away from viewing System 1 and System 2 processes in terms of defining lists of features to focusing instead on typical correlates of each kind of process. For example, System 1 is typically correlated with fast speeds, parallel processing, and automaticity, whereas System 2 is typically correlated with slow speeds, serial processing, and control. However, the only features that the authors see as defining are that System 1 is autonomous and does not require working memory, whereas System 2 requires working memory and engages in mental simulation.

Originally, the dual-process framework proposed that System 2 processes monitor System 1 outputs, detect errors, and correct them. More recent perspectives on dual-process theory emphasize that effective reasoning is not always corrective – processes that were traditionally characterized as needing deliberative processing can be cued in System 1 to provide “logical” intuitive responses (De Neys & Pennycook, 2019). Importantly, recent approaches to dual-process theory do not emphasize that intuitive (System 1) processes are inaccurate and deliberative (System 2) processes accurate. A range of evidence and theorizing proposes that System 1 can produce effective responses without correction and that System 2 can reach poor responses despite reflection (Morewedge & Kahneman, 2010; Pennycook, De Neys, Evans, Stanovich & Thompson, 2018). We find support for this assertion in our data – participants’ fast responses are often accurate. We study whether slow thinking is an effective means by which participants can improve their reasoning.

The rule-based approach and dual process approach emphasize different aspects of reasoning but are not mutually exclusive. As discussed earlier, slowing down may help in general, but may also be more helpful if one has access to the relevant rule. In fact, Sloman’s (1996) original description of System 2, which he called “rule-based,” assumed that its greater accuracy comes in part from accessing and using appropriate analytic rules for solving problems. The literature has introduced the terms ‘cognitive capital’ (Camerer & Hogarth, 1999) and ‘mindware’ (Perkins, 1995; Stanovich & West, 2008) to capture the rules, knowledge, and thinking styles that decision makers bring to a problem. These are both superordinate terms that include both knowledge (such as statistical rules) and individual differences such as thinking dispositions. For example, Stanovich and West (2008, p. 688) characterize mindware as the context specific “tools to think scientifically and the propensity to do so; the tendency to think logically; and knowledge of some special rules of formal reasoning and good argumentation” [italics added]. In the present research, we aim to disentangle the tools of reasoning, such as rules, from the propensity to use them. We review the dual-process and rule-based approaches to improving decisions, each of which emphasizes a different element of mindware (or cognitive capital). As we proceed, we integrate the approaches to develop a set of questions related to decision speed and rule accessibility. Later, we present the results of a large, multistage online experiment designed to determine the degree to which telling people to slow down is good advice.

2.1 System 2: Reflection, correction, and decision speed

Research using the dual-process framework has focused primarily on the reflection property of System 2. This includes both research into the benefits of slow thinking, and research asking whether slow thinking is needed at all. Recent research into problem solving in JDM proposes that deliberation plays a key role, but may be more important in choosing between competing intuitions, rather than calculating normative responses to substitute for an incorrect intuition (De Neys & Pennycook, 2019). In the present research, we emphasize another aspect of System 2. In its original description (Kahneman, 2000; Sloman, 1996; Stanovich & West, 1999), System 2 depends on rules to structure the reasoning process. We start our review of relevant literatures by focusing on the larger, more recent literature on reflection before turning to the older literature on rule possession in the next section. Our empirical tests will consider both of these properties of System 2. Not all judgment and decision making problems rely on inferential rules, but in the present research we focus on statistical reasoning problems with clear normative standards that depend on a specific, corresponding rule.

Researchers have investigated the impact of fast (System 1) thinking and slow (System 2) thinking using two main methods: individual differences in thinking style and experimental manipulations of decision speed.

The first line of evidence uses the Cognitive Reflection Test (CRT) as an individual difference measure. The CRT consists of three questions that have a tempting intuitive answer that happens to be incorrect. The CRT was originally offered as a measure of an individual difference in the tendency to override incorrect initial intuitive answers with deliberation (Frederick, 2005). More recently, scholars have suggested alternative ideas about what the CRT actually measures. Baron and his colleagues suggest that the CRT measures the degree to which one has a reflective cognitive style — a disposition that permeates all phases of problem solving (Baron, Scott, Fincher & Metz, 2015). Attali and Bar-Hillel (2020) contend that the CRT measures math ability; in their studies the CRT questions load onto the same latent construct as math questions that do not have tempting but incorrect answers (see also Erceg, Galić & Ružojčić, 2020, for similar conclusions).

As of this writing, exactly what aspect of cognitive style the CRT actually measures is still hotly debated. Regardless, it is a widely used measure and is associated with better performance in a range of reasoning problems, such as more patient temporal discounting (Frederick, 2005; Oeschssler et al., 2009) and greater reliance on expected values (Frederick, 2005; Cokely & Kelley, 2009), base rates (Oeschssler et al., 2009), and the law of large numbers (Obrecht et al., 2009). The CRT is also associated with reduced susceptibility to framing effects (Frederick, 2005), the conjunction fallacy (Oeschssler et al., 2009), and probability matching behavior (Koehler & James, 2010). However, the CRT has been found to be unrelated to anchoring effects (Oeschssler et al., 2009), frequency bias (Obrecht et al., 2009), and the bias blind spot (West, Meserve & Stanovich, 2012). These mixed results may be due to the source of errors: whether errors are strategy-based, association-based, or psychophysically-based (Arkes, 1991). For further discussion, see Toplak, West and Stanovich’s (2011) comprehensive review of the relationship between the CRT and performance in reasoning problems.

In the present research, we included the CRT with the expectation it would have a positive and significant relationship to performance on our JDM questions. Moreover, because of its common usage, the CRT provides a useful benchmark that would allow us to compare the relative effect sizes of movements between levels of CRT score with the effect sizes of behavioral interventions to encourage slow thinking. The results can shed light on whether a debiasing strategy of instructing reasoners to slow down is able to achieve a benefit similar to those observed for dispositional differences in reflection as measured by CRT. We also tested whether CRT and other individual difference measures interact with a less studied component of System 2 to enhance performance: rule accessibility. We will discuss this more fully in the next section.

In addition to using the CRT as an individual difference measure of thinking style, researchers have investigated the effect of thinking speed using two kinds of between-subjects experimental manipulations. The first paradigm compares conditions in which respondents think quickly and intuitively to conditions in which they think slowly and analytically. The second paradigm compares conditions in which respondents think quickly and intuitively with a control condition. Between-subjects manipulations of decision speed have been implemented across a wide range of problems, including probability matching (Roberts & Newton, 2001), conjunction fallacy (Villejoubert, 2009), belief bias (Evans & Curtis-Holmes, 2005; Tsujii & Watanabe, 2010), conditional inference (Evans, Handley & Bacon, 2009), and syllogistic reasoning (Stupple, Ball & Ellis, 2013). They have also been implemented with measures from a variety of applied areas, including marketing (Cryder et al., 2017), moral decision making (Phillips & Cushman, 2017), and economics (Rand, Greene & Nowak, 2012; Rand et al., 2014). Generally, researchers find significant effects comparing both fast versus slow conditions and fast versus control conditions, such that speeding up participants hurts their performance relative to the comparison group. Research on cognitive load has similarly found that limiting capacity impairs performance on reasoning problems, analogous to the effects of fast thinking (e.g., De Neys & Verschueren, 2006; De Neys, Schaeken & d’Ydewalle, 2005; De Neys, 2006; De Neys & Schaeken, 2007).

Decision speed has also been manipulated as a within-subjects variable, where subjects provide two sequential responses. In this paradigm, participants respond first with a fast, intuitive answer and then subsequently reflect on their initial response to provide a final answer (e.g., Thompson, Prowse Turner & Pennycook, 2011; Pennycook, Cheyne, Barr, Koehler & Fugelsang, 2014; Pennycook, Trippas, Handley & Thompson, 2013; Bago & De Neys, 2017; Koriat & Goldsmith, 1996; Shynkaruk & Thompson, 2006). The two-response paradigm has been used to research dual-system processes across reasoning problems, including base rates (Pennycook & Thompson, 2012; Pennycook et al., 2013), causal reasoning, denominator neglect, categorical syllogisms (Thompson & Johnson, 2014), rule and belief-based reasoning (Newman, Gibb & Thompson, 2017), syllogistic reasoning problems (Bago & De Neys, 2017), and the bat-and-ball problem from the CRT (Bago & De Neys, 2019b).

In sum, manipulations of decision speed have focused on comparing a fast condition with either a slow condition or a control. We do not know of any studies that compare a slow condition to a control condition, though in a conceptually similar line of work researchers have compared the instructions to “think logically” with a control group and found a benefit on performance in logical reasoning problems (Evans, Newstead, Allen & Pollard, 1994; Daniel & Klaczynski, 2006; Vadeboncoeur & Markovits, 1999; Evans, Handley, Neilens & Over, 2010; De Neys, Schaeken & d’Ydewalle, 2005). To our knowledge there are no papers including a fast thinking, slow thinking, and control condition in the study of decision making problems. Consequently, existing findings do not allow us to assess whether fast thinking hurts performance, slow thinking benefits performance, or both.

Does slow thinking improve performance relative to a control condition in which people think at their own, self-directed pace? We believe the answer to this question is critical for prescriptions for improving decision making. If interventions to encourage slow thinking are indeed helpful, such interventions would represent a readily implementable recommendation for improving decisions (as suggested in the recent articles mentioned in the opening paragraph). If the disparity between fast thinking and slow thinking is driven by the harm of being sped up, rather than the benefit of being slowed down, encouraging slow thinking is of less value. We believe that to make any argument about the benefits of slow thinking, we must first seek to assess it independently of fast thinking. In a similar argument, Payne, Samper, Bettman and Luce (2008) showed that earlier demonstrations of the superiority of unconscious decision making were artifacts of requiring decision makers in the conscious condition to deviate from their normal process by taking an inordinate amount of time to make their decision. The unconscious condition performed no better than the control condition in which respondents used their ordinary approach to decision making. We pose a similar question: Does slow thinking perform better or the same as a control condition in which respondents use their ordinary approach to decision making?

We investigated our research questions in a high powered, pre-registered experiment with pre-registered hypotheses. We frame these as questions rather than hypotheses – questions grounded in the literature and to which the answers are of general interest, regardless of their outcome. (Our pre-registration can be found at https://osf.io/34uxz.)

We tested participants on canonical JDM problems that highlight biased statistical reasoning. For example, we included the Linda problem from the introduction which shows that many people commit the conjunction fallacy. We focus on these kinds of problem because they served as foundational demonstrations in the development of the field of JDM (Kahneman, 2011). We include six different JDM biases in our study, including the conjunction fallacy and others that will be described later.

Our first two questions concern whether we will replicate past research relating CRT score to performance in canonical JDM problems, and whether we will replicate past research comparing the performance benefits of slow thinking versus fast thinking.

Question 1:

Are people more accurate on JDM problems when they score more highly on individual difference measures such as the CRT?

Question 2:

Are people more accurate on JDM problems in a slow thinking condition than in a fast thinking condition?

To test whether it is fast thinking that hurts performance, slow thinking that benefits it, or both, we test performance in each intervention groups against a control group in a between-subjects design.

Question 3a:

Are people less accurate on JDM problems in a fast thinking condition compared to a control condition?

Question 3b:

Are people more accurate on JDM problems in a slow thinking condition compared to a control condition?

Note that, based on the extensive past research we have reviewed, there is very good reason to expect a positive answer to Question 3a. The literature provides less guidance on Question 3b, as there has been very limited use of a control condition in studies that attempt to manipulate the degree to which people rely on fast thinking versus slow thinking.

It is possible that the benefit of slow thinking is more capable of being realized when an individual has access to the appropriate rule. In the next section, we develop questions that specify the conditional nature of System 2’s success.

2.2 System 2: Rule-based reasoning

In Kahneman’s (2011) description of System 2, one of its primary functions is to monitor and correct the automatic output of System 1. The ability for System 2 to monitor and correct flawed intuition depends on an additional feature of System 2: timely access to the relevant rule for solving the problem. Kahneman (2000) earlier proposed, “A task will be too difficult if (1) System 1 favors an incorrect answer, and (2) System 2 is incapable of applying the correct rule, either because the rule is unknown or because the cues that would evoke it are absent” (p. 682). This role for rule-based reasoning echoes Sloman’s (1996) original theorizing. Sloman (1996) called System 2 “the rule-based system” and argued that System 2 not only deliberates and verifies, but also accesses abstract knowledge derived from culture, education, and experience. Sloman (1996) described rules as symbolic structures that state relationships between variables; variables can take on new values in new situations (see also Smith, Langston & Nisbett, 1992). Rules thus have the important property that they are general — the reasoner can potentially apply them across different types of situations if they are accessed and recognized as relevant.

To illustrate some of the challenges that people face in applying rules, consider earlier research by Nisbett and his colleagues on statistical reasoning (Fong et al., 1986; Nisbett et al, 1987; Nisbett, 1993; Lehman, Lempert & Nisbett, 1988; Smith et al., 1992). This program of research argued that successful rule use depends on multiple factors, including access to the relevant rule, an ability to recognize when to use it, and an ability to use it in new domains with new variables (Nisbett, Krantz, Jepson & Kunda., 1983). For example, many people have good intuitions about sample size and regression to the mean in games of chance and in sports. They have access to the rule that larger samples are more reliable than smaller samples when outcomes have a clear stochastic element. However, in other domains it can be hard to recognize the relevance of a rule or how to apply it. Job interviews are small samples of noisy behavior that provide an imperfect glimpse into a person’s underlying traits. People neither recognize that behavior is a sample drawn from an underlying distribution nor that sample size is relevant to the problem. Linking back to the quote from Kahneman that opened this section, it is not enough to simply engage System 2, or even to have access to the rule. The decision problem must arrive with cues that bring the correct rule to mind, which in turn must be recognized as the correct rule to use in the situation. Nevertheless, having some form of access to the rule is necessary if not sufficient for solving the problem.

In other work, researchers have used neutral versions of problems to measure whether a decision maker has the necessary mindware to solve a problem (Stanovich & West, 2008). The aim of a neutral problem is to strip out content that is likely to evoke a heuristic-based, intuitive answer that is incorrect. In this way, the neutral problem provides a pure measure of whether or not the participant knows the rule needed to correctly solve the problem. For example, Frey, Johnson and De Neys (2018) asked two neutral problems about base-rates and two about conjunctions that removed misleading stereotype information. The total score (out of four) correlated significantly with whether subjects could be classified as a consistent detector of conflict across base-rate and conjunction study problems. Similarly, Šrol and De Neys (2020) constructed a mindware instantiation index by averaging performance across eight neutral reasoning problems. The index was significantly correlated with numeracy and cognitive ability as measured by the Vienna matrix test (Klose, Černochová & Král, 2002), and was also the single best predictor of accuracy on study questions that depended upon the same measured rules.

We aim to build on this existing research by disentangling two aspects of mindware: access to specific rules and the individual differences that contribute to successful application of this knowledge. In our study, we measured the accessibility of six different rules that each uniquely corresponds to one of our six JDM problems. Each rule was measured with a problem structure that was relatively transparent so that if subjects had access to the rule, they would be likely to answer the rule question correctly. These transparent questions are similar to the neutral problems used in Frey et al. (2018) and Šrol and De Neys (2020); our main point of departure was to test the degree to which access to specific rules helped with directly corresponding JDM questions that were more difficult and less transparent. We ask whether access to the relevant inferential rule will positively predict problem performance on its related JDM question.

Question 4:

Are people who have access to a specific inferential rule more accurate on directly related JDM problems compared to people who do not have access to the rule?

We are interested in the relationship between access to inferential rules and performance in reasoning tasks, as this has implications for debiasing interventions. As we measure access to six different rules, our design allows us to distinguish between the effects of general rule access and problem-specific rule access. This affords us insights to the process by which respondents access and apply knowledge to focal problems. If rule accessibility is tied to a general store of knowledge and not to specific rules, then the predictive power of having access to the appropriate rule for a JDM problem should on average be no greater than the predictive power of having access to other rules that are necessary for other types of JDM problems. For example, if specificity is irrelevant, then access to the probability matching rule should be equally as predictive of success in the Linda problem as is access to the conjunction rule. We will show that, although general rule accessibility is predictive, access to the specific rule is also important. We suggest that this is strong evidence for a rule-based account in which successful reasoners retrieve and apply abstract, necessary rules that they already know to some degree (when such rules exist).

2.3 Rules and decision speed

The reason that instructing people to slow down might help performance in JDM problems is that it causes them to correct or replace an erroneous but intuitively tempting answer. This is more likely to happen if they have sufficient access to the necessary rule for solving the problem. We examine the combined benefit of rule knowledge and reflection by first examining reflection as an individual disposition (as measured by CRT).

Question 5:

Does having access to a specific rule increase the benefits to accuracy associated with having a more reflective disposition (as measured by the CRT)?

Similarly, we ask whether our intervention to engage in slow thinking may be of greater benefit among those with access to the inferential rule.

Question 6a:

Does having access to a specific rule increase the accuracy benefits of a slow thinking condition relative to a control condition?

Conversely, even if one has access to the rule, one may not be able to apply it if required to make a decision very quickly. For individuals who have access to the rule, fast decision making may tend to prevent application of the rule and cause them to fall back on incorrect intuitions. An important boundary condition to this perspective is that reasoners may have rules sufficiently encoded that they produce accurate intuitive responses (Frey et al., 2018; Šrol & De Neys, 2020).

Broadly, people can be divided into at least three categories of knowledge: Experts who can immediately generate good responses (Larrick & Feiler, 2015), people who do not have access to the relevant rule, and individuals who require more deliberative processes to access and apply a rule. For the first and second categories, performance should not be affected by behavioral manipulations of decision speed. Experts should be able to generate correct answers quickly. For individuals who lack access to the rule, their decision will be poor regardless of decision speed. For the third category, faster thinking is likely to be harmful if it disrupts their ability to access and apply an inferential rule. We ask whether the effect of a fast thinking manipulation varies with participants’ access to inferential rules by testing the interaction described in Question 6b.

Question 6b:

Does having access to a specific rule increase the cost to accuracy of a fast thinking condition relative to a control condition?

2.4 Incentives

If slower thinking improves accuracy on JDM problems, then one might argue that providing monetary incentives for correct answers should have the same effect. In the absence of incentives, people may take cognitive shortcuts because the effort needed to correctly solve the problem is not worth expending. With incentives, decision makers should be willing to expend more effort to solve the problem correctly.

Although incentives might spur people to try harder, a number of studies have concluded that incentives do not appreciably reduce susceptibility to biases (see Camerer & Hogarth, 1999, for a review). This is true even of very large incentives. Recently, Enke et al. (2020) conducted a study in Nairobi, Kenya, where they rewarded participants with the equivalent to one month’s salary for answering questions correctly. They tested susceptibility to several biases, including base rate neglect and anchoring. Not surprisingly, participants took substantially more time when incentives were very large — a reflection of greater effort. Nevertheless, solution rates remained largely unchanged for five of the six tasks. Although participants may have tried harder, their performance likely did not improve because the incentives did not instantaneously confer the correct mental representation or rule for solving the problem (Payne, Bettman & Johnson, 1992; Epley & Gilovich, 2005).

There was one exception to this finding — with very large incentives, performance on the CRT increased from around 35% in the control condition to 48% in the incentive condition. The CRT stands in contrast to many other cognitive tests in that most people can probably access the needed skills to solve at least one of the problems (basic addition and subtraction are needed to solve the bat-and-ball problem). Enke et al.’s (2020) results suggest that incentives improve performance when people have the necessary rules and skills to produce the correct answer but do not improve performance when rules and skills are lacking.

For the purpose of comparison, we included an incentives condition in our experiment. Notably, Enke et al.’s (2020) participants did not take more time when presented with standard laboratory incentives than in a no-pay control condition. We suspect, however, that relatively small incentives may be more effective at inducing thoughtfulness with online participants when the incentives are non-trivial relative to the base pay. The inclusion of an incentives condition will allow us to compare slow thinking to incentives in terms of time taken, performance, and interaction with rule accessibility. If the two conditions have similar effects, it would seem reasonable to infer that incentives cause people to slow down and think harder, much the same as we instruct people to do in the slow thinking condition.

Question 7:

Are people more accurate on JDM problems in an incentive condition compared to a control condition?

3 Experiment

Our primary goal in this research is to evaluate whether telling people to slow down their thinking is good advice for canonical statistical problems in the JDM literature. This is a different question from asking whether people are more accurate when they think more slowly. People might slow down on their own, for instance, when it is appropriate to do so (Payne et al., 2008). They might also slow down due to dispositional differences (such as those captured by high CRT scores). We are interested specifically in whether it helps to encourage slow thinking when respondents are acting as they would naturally. Furthermore, our review of the literature suggests that even if the advice to slow down helps in the aggregate, it may help people differentially depending on their individual dispositions and the rule knowledge to which they have access. Thus, we formulated questions relating to both main effects and interactions to ask whether encouraging slow thinking may work better for some people than for others.

Empirically, we will try to distinguish between knowledge and individual differences in cognitive dispositions in our experiment. For clarity, we will use different terms for each of these two aspects in our operationalization: inferential rules and individual differences, respectively. We measure accessibility to the specific, rule-based knowledge needed to solve a focal JDM problem (e.g., the conjunction rule); and we measure decision making disposition using individual differences such as performance on the CRT. This will allow us to look at the effects of our manipulations when including these variables in the model, and also ask several additional questions. For example, we tested whether high CRT individuals would answer more canonical JDM problems correctly, and whether this advantage would be more pronounced when they have access to the related statistical rule.

We designed a single, high-powered experiment that facilitates answering our questions. Participants completed two separate stages that were completed at least 24 hours apart. This was intended to reduce fatigue and to mitigate any contamination of our dependent measures by our inferential rule measures. In the first stage, participants completed the 12 inferential rule questions (6 rules x 2 measures each) and the questions from the CRT, CRT-2 and Berlin Numeracy Test (BNT), as described in more detail below. In Stage 2, the participants responded to the 12 JDM questions that served as our DVs (6 JDM problems x 2 measures each). We measured access to each inferential rule and each JDM problem twice to reduce measurement error.

3.1 Method

3.1.1 Materials

We needed three categories of problems in order to find the answers to our questions: problems that test for JDM biases that appear in the literature, problems that test for access to rules, and problems that test for individual differences in cognitive disposition. We next describe briefly each set of problems and how they were constructed. Full experimental materials are available in an online repository at https://osf.io/mnvej/.

Problems to test JDM biases

To construct our battery of JDM questions, we started with 31 judgment and decision making problems and principles from four comprehensive review papers (Stanovich & West, 2000; Stanovich & West, 2008; Parker & Fischhoff, 2005; Bruine de Bruine, Parker & Fischhoff, 2007). We selected problems that had a clear normative principle to apply. This led to the exclusion of a large number of framing problems, which test the internal consistency of preferences across different representations as opposed to the application of a rule. (For example, gain-loss framing effects indicate inconsistent risk preferences, but there is no normative answer for a given risk taking frame.) Furthermore, we focused on problems with statistical principles over logical reasoning problems, as the former have been more central in traditional JDM research. We caution against generalization to broader categories of problems (e.g., non-statistical problems) or situations (e.g., choices based on subjective preferences).

Our search process led us to select problems that illustrate six classic JDM biases: the conjunction fallacy (Tversky & Kahneman, 1983), probability matching (Stanovich & West, 2008), default bias (Ritov & Baron, 1990), base rate neglect (Kahneman & Tverksy, 1973), denominator neglect (Kirkpatrick & Epstein, 1992), and Cell A bias in covariation problems (Wasserman, Dorner & Kao, 1990). Although we closely modeled our problems on the ones from the above-cited sources, we modified them to a greater or lesser extent, for three different reasons. First, we needed problems that could be coded as clearly correct or incorrect. This created a special issue for the base rate neglect problem, so we had to use a revised version. Second, we needed to ensure that baseline performance in the control condition was at least as accurate as random responding. If it were not, any improvement in performance could potentially be explained by an increased rate of random responding rather than more normative problem performance. Third, our procedure called for two versions of each type of problem to reduce measurement error. We therefore constructed a second version of each problem keeping the same structure but changing the content.

Problems to test access to inferential rules

A number of scholars have pointed out that to solve many JDM problems one has to, at a minimum, have access to the relevant statistical rule (Kahneman, 2000; Nisbett, 1993; Stanovich & West, 2008). What does it mean to have access to a rule? One version of accessing a rule is that a person can retrieve and apply an abstract representation of the formal normative rule (e.g., P(A) ≤ P(A∩B) for conjunctions). Another version is that a person has learned exemplars of the rule through experience and generalizes from that experience when encountering new problems. Nisbett (1993) and colleagues argued that rules can be learned and stored at a level that is easily applied and generalized in everyday contexts; people have a harder time learning and understanding abstract rules stated as mathematical or logical relationships. For example, Cheng and Holyoak (1985) showed that people can accurately test relationships that involve permission and obligation (e.g., a customer can drink alcohol only if she is at least 18 years of age) that they fail to evaluate effectively when stated as an isomorphic logical principle (e.g., if p, then q). Thus, we chose not to ask people about direct statements of abstract rules. Instead, we measured whether a person could answer a simple and transparent problem that requires access to the rule. Our key goal in designing transparent problems was to minimize the presence of a tempting but wrong intuitive answer that competes with application of the rule.

Consider the Linda problem described in the introduction. This problem requires access to the conjunction rule. However, it also has a tempting incorrect answer because people tend to substitute assessments of similarity for probability. The key to testing access to the conjunction rule in this case is to remove the presence of a tempting incorrect answer. Consider the following Sally problem.

Imagine Sally owns a car.

Rank the following from most likely (=1) to least likely (=3):

1. (1) The car has Bluetooth speakers.

2. (2) The car is painted green.

3. (3) The car has Bluetooth speakers and is painted green.

Compared to Linda, there is less material provided with which to form an impression of Sally and the types of activities she might engage in. The Sally problem is transparent, so we count a person as having some access to the rule if he or she judges the third option as the least likely.

We included two transparent questions measuring rule accessibility for each of our six JDM problem types to reduce measurement error of rule accessibility. Of course, these do not provide a complete picture of a participant’s ability to retrieve and apply a rule across contexts. Yet, if a participant cannot answer questions accurately in these two transparent contexts, we argue that other individual differences such as a disposition to reflect are less helpful for correctly answering standard JDM questions in which intuition provides a conflicting response.

Problems to test individual differences

We measured individual differences primarily so that we could include these variables in our regression analysis when measuring the effects of fast and slow thinking. We were also interested in exploring certain interactions. For example, it is plausible that low CRT individuals would benefit more from a slow-thinking intervention because high CRT individuals already tend to engage in reflection. Including scales such as the CRT provided the opportunity to test for this. We included three scales: the three-question CRT (Frederick, 2005), the four-question CRT-2 (Thomson & Oppenheimer, 2016), and the four-question BNT (Cokely, Galesic, Schulz, Ghazal & Garcia-Retamero, 2012).

The CRT is intended to assess a respondent’s disposition to reflect on and potentially correct automatic System 1 responses. However, to perform well on the CRT, respondents must not only have the disposition to reflect, but they must also possess the knowledge to detect a possible need for correction and then implement that correction (Kahneman, 2000). As the problems on the CRT involve calculations (albeit relatively simple ones), the CRT likely has a numerical reasoning component. To directly assess a tendency to reflect, we also included the CRT-2 (Thomson & Oppenheimer, 2016), which does not depend on performing calculations to reach the correct answers. Finally, we included the Berlin Numeracy Test (Cokely et al., 2012). Many JDM problems are highly numeric and depend on such reasoning skills, so variation in numeracy would likely add noise to whether or not participants correctly solve a given JDM problem. Our primary motivation for including the BNT was so that we could include this variable in our regression analysis when studying the relationship between our behavioral interventions and the rate of successful problem solving.

3.1.2 Participants

We recruited participants with US IP addresses using Amazon’s Mechanical Turk platform (mTurk). Prospective participants were informed that they should participate only if they intended to complete both stages. In Stage 1 we collected 2,199 responses, excluding 203 participants for failing an attention check and 1 participant for failing to consent to return to Stage 2 of the study. For Stage 2 we invited 1,995 participants to return, collecting 1,869 responses. In Stage 2 we removed 147 participants who failed an attention check, and 7 who stated that they had not completed Stage 1. Both of these checks occurred at the start of the survey, prior to random assignment to a condition. Of the remaining 1,715 observations, we could match 1,709 participants’ Stage 2 responses to their responses in Stage 1. We excluded 3 participants for not answering a question from Stage 1. The resulting sample of 1,706 participants formed the basis of our study.

The study was posted in four batches (i.e., separate HITs in mTurk) of 500 people each in October 2019. Each HIT had a similar attrition rate between stages (12–16%). Stage 2 of each 500-person batch was made available 24 hours after the last member of the group completed Stage 1 and remained accessible for one week. On average, participants waited about two days before starting Stage 2 (M = 53.0 hours, SD = 24.1). The compensation for Stage 1 of the study was $1.00. The compensation for Stage 2 was $1.50, plus a bonus of $0.50 for returning to complete both stages, bringing total compensation to $3.00. Our sample was 45.6% female.

3.1.3 Procedure

Procedure: Stage 1.

Participants were informed that this study was Stage 1 of a two-stage study, and that they would be invited back to complete the second stage for additional income 24 hours after the initial HIT was completed. Participants were asked to identify their willingness and ability to return for Stage 2 at both the start and the end of the Stage 1 study.

The inferential rule questions were divided into two blocks of six, with each block containing one question for each rule. Participants began the study by completing one block of inferential rule questions. Which block they saw first was counterbalanced, as was the question order they saw within a block. Each participant saw questions in one of six possible rule orders that followed a Latin square design. These rule orders were the same in each block. For example, if the question associated with a given rule was presented in the k^th position in the first block, the other question associated with the same rule was presented in the k^th position in the second block.

After completing the first block, participants answered the 11 questions from the CRT, CRT-2, and BNT in a randomly presented order, determined by Qualtrics for each participant. Following this, they answered the six questions from the other inferential rule block. There were no transitions between these different parts of the study, so from the participants’ point of view they simply answered a sequence of 23 questions, each presented on a separate screen. Some questions contained multiple responses (e.g., the probability matching rule question). When a question contained multiple responses, all of these responses were placed on the same screen. After completing all the questions, participants reported their sex, age, and level of education. They also reported their mTurk identification number so that we could contact them for Stage 2.

Procedure: Stage 2.

Using TurkPrime’s inclusion function (Litman, Robinson & Abberbock, 2016), we invited all the participants who completed Stage 1 back for Stage 2 of the study. The JDM problems were divided into two blocks of six, with each block containing one of each of the six types of problems (the conjunction fallacy, probability matching, default bias, base rate neglect, denominator neglect, and Cell A bias in covariation problems), in a similar Latin square setup to Stage 1. As in Stage 1, each question appeared on its own screen. There were no filler questions between the two blocks.

Participants were randomly assigned to a problem type order condition that determined the order of the questions in each block (following a Latin square design), a block order condition, and a study condition.¹ The study conditions were control, Slow, Fast, Fast-slow (within-subjects), and Incentive. After being assigned to a study condition, participants were presented with instructions for the study. These included the behavioral manipulation associated with their study condition. We adapted the text for our conditions from previous work studying the impact of fast and slow responding (Bago & De Neys, 2017). Participants began by reading the instructions for their condition. These instructions were as follows:

Control Condition. In this task we’ll present you with a set of problems. We will ask you to respond to each problem with your best answer.

As each problem is presented, you can take all the time you want to indicate your response. It is important that you give your best responses to all the problems.

Slow Condition. In this task we’ll present you with a set of problems. We will ask you to respond to each problem after actively reflecting on it.

As each problem is presented, you can take all the time you want to actively reflect on it. Once you have made up your mind, you will then enter your final response. You will have as much time as you need to indicate your answer. As you read each problem, think about the possible answers to the problem and select the one that you feel is most likely to be correct. It is really crucial that you give your response after reflecting on each problem deeply.

Fast Condition. In this task we’ll present you with a set of problems. We will ask you to respond to each problem with your initial, intuitive answer.

As each problem is presented, you should answer with your initial response—the very first answer that comes to mind. You don’t need to think about it. Just give the first answer that intuitively comes to mind as quickly as possible. It is really crucial that you give your first, initial response as fast as possible.

Fast-slow Condition. In this task we’ll present you with a set of problems. We will ask you to respond to each problem twice. First, respond with your initial, intuitive answer. After submitting this answer, please respond to each problem again after actively reflecting on it.

As each problem is presented, you should answer with your initial response—the very first answer that comes to mind. You don’t need to think about it. Just give the first answer that intuitively comes to mind as quickly as possible. It is really crucial that you give your first, initial response as fast as possible. After this, you can take all the time you want to actively reflect on it. Once you have made up your mind, you will then enter your final response. You will have as much time as you need to indicate your answer. As you read each problem, think about the possible answers to the problem and select the one that you feel is most likely to be correct. It is really crucial that you give your final response after reflecting on each problem deeply.

Incentive Condition. In this task we’ll present you with a set of problems. You will be paid a bonus of $0.50 for a correct answer in a randomly selected question.

As each problem is presented, you should answer with the response that gives you the best chance of earning the bonus payment. Once you have made up your mind, you will enter your final response. You can take all the time you want to indicate your response. It is really crucial to answer problems correctly to increase your chances of winning the bonus payment.

Manipulations

To reinforce the manipulations, participants were asked to respond to an open-ended question asking for their interpretation and understanding of the manipulation. Before beginning to answer the problems, participants were asked to state how willing they were to comply with the experimental instructions, for example, ‘How willing are you to keep answering each problem as fast as possible with the first answer that comes to mind, then answering again after reflecting on the problem deeply?’ Participants indicated on a sliding scale from 0 to 100 how willing they were to continue to comply with these instructions. After completing their first block of six JDM questions, participants were then asked to recommit to the experimental instructions. Participants then continued to answer the second block of six JDM questions.

Full details of the study manipulations are included in the supplement. The structure for the study was similar to that of Stage 1. Of the resulting variables, Order denotes one of the six Stage 2 problem type orders from the Latin square, Block Order denotes whether the focal question was presented in the first or second block of JDM questions, and Measure denotes which of the two measures the observation corresponds to within a problem type (e.g., there were two conjunction fallacy problems: the Linda question, or the Bill the accountant question, Table 1). Our initial analyses focused on comparisons among control, Fast, Slow, and Incentive conditions (n = 1471). (Subsequent analyses include tests using the Fast and Slow responses from the Fast-slow within-subjects condition.)

Table 1: The two inferential rule questions (Stage 1) and two JDM questions (Stage 2) for the conjunction fallacy problem.

3.2 Results

3.2.1 Analytical approach

We used dummy-coded condition variables and continuous individual difference variables to predict performance on our JDM problems at a question level. Each participant provided 12 responses to JDM problem questions. Responses to the three questions of the CRT (Frederick, 2005) were coded into a score between 0 and 3. Responses to the four questions of the CRT-2 (Thomson & Oppenheimer, 2016) were coded into a score between 0 and 4. Responses to the four questions of the Berlin Numeracy Test (Cokely et al., 2012) were coded into a score between 0 and 4. We constructed a variable Rule _Specific that took the value of 0, 1 or 2, depending on how many of the inferential rule questions were answered correctly for a specific problem type. Note that Stage 1 measures of the specific inferential rules (two questions such as the Sally and Bill-playing-darts problems presented above) were measured independently of and at least 24 hours before Stage 2 measures of a JDM problem (two questions such as the Linda problem presented above). A participant’s score for the two measures that make up Rule _Specific were used to predict their performance on the two JDM problems that make up the DV corresponding to that inferential rule. Inferential rules, CRT, CRT-2, and BNT were mean-centered across the full sample (including the Fast-slow observations) for all of our analyses. Our dependent variable was whether or not a question was answered correctly.

For our analyses, we used Generalized Estimation Equations (GEE) to estimate logistic regression models. A GEE is used to estimate the parameters of a generalized linear model where outcomes may be correlated (e.g., responses nested within a subject). We clustered these data by participant. To conduct this analysis, we used the ‘geepack’ package (Hojsgaard, Halekoh & Yan, 2016) for R. We specified a binomial distribution family with a logit link, as our outcome data is binary, and specified an ‘exchangeable’ correlation between responses, following guidelines to minimize the Quasi Information Criterion (Hardin & Hilbe, 2003; Pan, 2001; Hin & Wang, 2009).

Our data contained two measures of each participant’s response to each of the six JDM problems. We included a Problem effect (for each of the 6 JDM problems) and a Measure effect for whether the problem answered was the first measure or the second (e.g., Linda the bank teller or Bill the accountant, right column, Table 1). We decomposed the Order variable into five dummy-coded Position effect variables (e.g., a dummy variable for third position would take the value of 1 if this question was presented in position 3 in its block, 0 otherwise), using first position as the omitted category. We also included a Block Order variable, signifying whether the question was in the block of JDM questions presented first or second. We do not report these nuisance factors in the main manuscript, but the full model estimates can be seen in the supplement.

3.2.2 Data analysis

Individual differences.

In Panel A of Figure 1, we plot the percentage of JDM questions answered correctly (out of 12) by score on the CRT (0, 1, 2, 3). Average performance was monotonically increasing in CRT, with a one-point increase in the CRT associated with a 9.5 percentage point increase in accuracy. All three of the marginal movements between CRT levels were statistically significant (p < 0.001) in predicting greater average accuracy across the 12 JDM questions. Across all conditions, participants with a CRT score of 0 had an average accuracy of 42.0%, which rose to 70.4% for participants with a CRT score of 3. Given that the α of the full 11 questions from our individual difference measures (CRT, CRT-2, and BNT) was 0.77, we also plotted the average number of JDM questions answered correctly by score out of the 11 pooled individual difference questions (Figure S1 in the supplement).

Figure 1: The average accuracy across 12 problems by CRT score (Panel A) and study condition (Panel B). Note. Error bars indicate plus or minus 1 standard error. The cell size and mean and standard deviation of the percentage of JDM questions answered correctly is indicated on the bars. fast_WS refers to the within-subjects fast response, fast_BS to the between-subjects fast condition, slow_WS refers to the within-subjects slow response, and slow_BS to the between-subjects slow condition.

We found that CRT, CRT-2 and BNT all explained unique variance in performance in our battery of JDM questions. Whether we introduced each individual difference measure by itself or included all three measures, we found that all of the individual difference measures were statistically significant positive predictors of success on our JDM questions (p < 0.001; Models 2–5; Table 2). Based on this evidence, we find positive support for Question 1 – higher scores on individual difference measures including the CRT were associated with higher accuracy on JDM questions.

Table 2: Logistic regressions predicting success with intervention conditions coded relative to control and with individual differences mean centered.

Note.

^*** p < 0.001

^** p < 0.01

^* p < 0.05

^† p < 0.10

The coefficient estimates for Measure, Problem, Position, and Block Order effects are included in the SI (Table S1).

Fast thinking, slow thinking, and control.

Manipulation check.

We performed two manipulation checks to test the efficacy of our Fast versus Slow manipulations. First, in a separate pilot, we tested whether our manipulations were effective in changing performance in the bat-and-ball task (Frederick, 2005) in a between-subjects design. This question was answered correctly by 29 of 83 (35%) participants in the Slow condition, compared to 23 of 106 (22%) participants in the Fast condition (Fisher’s exact p = 0.050). The pilot also included a separate Fast-slow within-subjects condition. Here, only 8 of 88 (9%) answered the question correctly on their initial fast answer, whereas 28 (32%) answered it correctly on their final slow answer (McNemar’s χ 2 = 38.2, p < 0.001).² These tests provide evidence that our behavioral interventions can replicate previously observed effects in improving performance in problems.

Our second manipulation check examined the average time taken on the JDM questions across conditions in Stage 2 (Table 3). The average log time taken on the JDM questions was significantly longer in the Slow condition relative to both the Fast condition (p < 0.001) and the control condition (p < 0.001). The average time taken in the control and Incentive conditions were similar and landed between the Fast and Slow conditions. We conclude that our Fast and Slow manipulations had the intended effect on time spent answering our questions.

Table 3: Descriptive Statistics of JDM Question Performance and Log Time Taken in the Between-Subjects Sample. (N = 1471.)

Note. JDM Questions Correct is the average number of JDM questions answered correctly (out of 12). Average log time is the average of the log time taken to provide a response to a JDM question within a condition. Exp (avg. log time) is this average exponentiated. Follow % is the average response participants’ provided to a self-report regarding the extent to which they followed our experimental instructions, on a percentage scale from 0 to 100. Rules_Total is the average number of inferential rule questions answered correctly (out of 12).

Tests of Slow versus Fast

Question 2 asked whether slow thinking would lead to more accurate decisions than fast thinking. For this analysis, we tested dummy-coded conditions against the Fast condition, which was the omitted category. Model 6 of Table 4 shows that participants in the Slow condition were significantly more accurate than those in the Fast condition (b = 0.532, p < 0.001). Model 6 also shows that participants in the control condition were significantly more accurate than participants in the Fast condition (b = 0.377, p < 0.001). Participants in the Fast condition had an average accuracy of 52.2%, relative to 58.9% in the control condition and 61.6% in the Slow condition. In recent meta-analytic work (Rand, 2019), researchers found that the difference between intuitive and deliberative thinking conditions on the rate of cooperation in economic games ranged from 1.6-3.1 percentage points. In our context, we find a 9.4 percentage point difference between Fast and Slow thinking conditions. This is a larger effect.

Table 4: Logistic regressions predicting success with conditions coded relative to Fast and with individual differences mean centered

Note.

^*** p < 0.001

^** p < 0.01

^* p < 0.05

^† p < 0.10

The coefficient estimates for Measure, Problem, Position, and Block Order effects are included in the SI (Table S2).

A good deal of previous research has used an individual difference, CRT, to demonstrate the benefits of fast thinking and slow thinking. Figure 1, Panel A, shows similar benefits in these data. Our current design allows us to assess the degree to which experimental interventions have a similar impact to those shown using CRT. To examine this, we plotted the average percentage of JDM questions answered correctly out of 12 by study condition in Figure 1, Panel B. The difference in average percent correct between our between-subjects Fast and Slow conditions (9.4%) was approximately equal to the difference between each ascending pair of averages grouped by CRT score (9.5%). In other words, the average difference in performance between asking respondents to engage in fast thinking and slow thinking was approximately equivalent to the average difference in performance between two respondents whose CRT scores differ by one point.

We note that even when engaging in slow thinking, many participants failed to answer problems correctly; even when engaging in fast thinking, many participants reached the correct answers. In our data many people reasoned well intuitively, consistent with recent accounts of the “smart intuitor” (Raoelison, Thompson & De Neys, 2020). For reference, across all five conditions there were 23 participants who answered zero individual difference questions correctly, who achieved an average accuracy across the 12 JDM questions of 29.7%. Relative to this level of performance (29.7% accuracy) participants in the Fast condition were considerably more successful (52.2% accuracy).

The strength of these effects varied to a modest degree across our six JDM problems. The greatest difference between our Fast and Slow conditions was observed for the denominator neglect question; the smallest difference was seen for the default bias problem (see Table S3 in the supplement for further details).

Tests of Fast and Slow versus the control

In order to identify the specific effects of fast thinking and slow thinking, we ran analyses using dummy-coded intervention variables with the control group coded as the omitted category. In Table 2 we present estimates of the effects of our different behavioral interventions.

We found a robust, negative effect of our Fast manipulation on the likelihood of responding correctly in our JDM questions (p < 0.001; Models 1-5). This suggests that the answer to Question 3a is yes – encouraging fast thinking does hurt performance relative to the control level. However, the effect of our slow thinking manipulation was more dependent on model specification. The coefficient on our Slow manipulation was positive, but attained statistical significance only in Model 5 (b = 0.155, p = 0.049). This result provides an equivocal answer to Question 3b. There was a small effect of our slow thinking manipulation relative to the control. The coefficient’s magnitude was similar across models. However, it reached a p-value of .05 only after controlling for all of the individual difference measures (CRT, CRT-2, and BNT) simultaneously. Later analyses (Table 5) that include Rule variables show a smaller coefficient for Slow and the Slow condition is not significantly different from the control in any specification. We see in Table 3 that this is likely due to participants in the Slow condition performing slightly better on Rule items than did participants in the control condition.

Table 5: Logistic regressions predicting success with conditions coded relative to control and with individual differences mean centered.

Note.

^*** p < 0.001

^** p < 0.01

^* p < 0.05

^† p < 0.10

The coefficient estimates for Measure, Problem, Position, and Block Order effects are included in the SI (Table S9).

Our results support the general conclusion that fast thinking hurts, and slow thinking helps. But the magnitude of the coefficients suggest that the effects are not symmetric relative to the control. Whereas the intervention Fast harmed performance accuracy by 6.7 percentage points, Slow yielded a gain of only 2.7 percentage points, relative to the control. We believed that participants may be more motivated to respond quickly (which is easier) than slowly and thoughtfully (which is more effortful and costly). Consequently, it is possible that participants in the Fast condition may have complied with our experimental manipulations to a greater degree than those in the Slow condition. To explore this possibility, we conducted several robustness checks where we trimmed the data based on either response time or self-reported compliance (Table S4). The results of these models were broadly consistent with the trends we see in the main analyses—Fast appears to harm performance more than Slow helps across multiple subsamples of the data that attempt to address compliance issues in different ways.

We also looked for problem-level differences in the benefits of slow thinking relative to a control. There is some evidence that there is a benefit to Slow thinking relative to the control for the base rate problem (77% correct versus 71% correct). See Table S3 for participants’ accuracy in each problem across our conditions. The base rate problem differed somewhat from our other questions, in that the coding of a correct answer required setting a threshold for a correct answer that implied a normative likelihood ratio. We augment our main analyses by providing analysis of the raw responses (i.e. the probabilities participants provided) to each of the base rate questions in Table S5. We found that our Slow manipulation negatively predicted participants’ estimated probabilities (i.e., indicated smaller deviations from the base rate of 10%) for measure 1 but not measure 2 of our measure of performance in base rate problems. We are reluctant to draw any conclusions from inspecting one question out of our original 12.

Access to inferential rules.

One question of primary interest in the present research was whether problem-specific rule knowledge would significantly predict performance in a matched problem that requires knowledge of that specific rule. We distinguish between three different variables in our regression analyses; Rule _Specific, Rule _Total, and Rule _Non-specific. When considering a single measure of a single JDM problem (for example the Linda version of the conjunction problem), a participant had a score out of 2 denoting how many of the corresponding Rule questions they answered correctly (Rule _Specific). That participant also had a score out of 12 for how many Rule questions they answered correctly in total across all problem types (Rule _Total). We computed the difference between these two scores to get the number of non-focal rule questions the participant answered correctly, as a score out of 10 (Rule _Non-specific). In all of our models that make reference to Rule _Specific, we also include this variable Rule _Non-specific.

To confirm that the two questions making up the Rule _Specific measure were in fact tapping into a construct that was similar, but different from general rule knowledge, we assessed two correlations: those between the two related questions and those between all combinations of unrelated questions. We found that the average correlation between the two measures of the same rule was r = 0.50, whereas the average correlation between measures of different rules was r = 0.27 (see Table S6 in the SI). The higher correlations between our measures of the same rule are suggestive that our Rule _Specific variable does measure something specific to their matched problems, rather than general statistical knowledge.

Table 4, Model 7 shows that having access to a specific rule (RuleSpecific) predicted better performance on its related JDM problem (b = 0.577; p < 0.001) when including CRT, CRT2, BNT and RuleNon-specific in the regression equation. Having non-specific Rule knowledge appeared to be beneficial as well (b = 0.185; p < 0.001).

Table 4, Model 7 shows that having access to a specific rule (Rule _Specific) predicted better performance on its related JDM problem (b = 0.577; p < 0.001) when including CRT, CRT2, BNT, and Rule _Non-specific in the regression equation. Having non-specific knowledge appeared to be beneficial as well (b = 0.185; p < 0.001).

A complication in interpreting the relative magnitudes of the rule coefficients in Model 7 is that the rule scales include different numbers of items. To address this, we ran additional regressions comparing the coefficients of Rule _Specific with that of a 2-item non-specific rule measuring access to a randomly selected rule from the other five rules—Rule _RAND. Across 500 different randomly drawn sequences of Rule _RAND, the coefficient on Rule _Specific had a mean of 0.579 and a SD of 0.0042. In contrast, the coefficient on Rule _RAND, had a mean of 0.1726 and a SD of 0.0283. The coefficient for Rule _Specific was larger in all 500 regressions. Having specific rule knowledge clearly improved performance more than general statistical knowledge as measured by randomly-drawn non-specific rule items. See the Additional Analysis in the supplement for further details.

To put the effect size of our Rule _Specific and Rule _Non-specific questions in context, we evaluated average performance at different levels of Rule _Specific (0, 1, 2) and compared it to the average performance at different levels of performance in other inferential rule items, on a comparable scale from 0 to 2. In our control condition, average accuracy on JDM questions ranged from 26.5% with a Rule _Specific score of 0 to 68.5% with a Rule _Specific score of 2, a change of 42 percentage points. Averaged across the results for the other five, non-focal Rule measures (i.e., each two-item measure of a non-specific Rule), performance ranged from 35.6% at a score of 0 to 66.3% at a score of 2, a change of 30.7 percentage points. These results further show that specific rule knowledge appears to have a larger benefit than the benefit associated with whatever general statistical knowledge to which one might have access.

In Question 4 we asked whether access to a specific inferential rule measured in a simpler, more transparent context questions (such as answering the transparent conjunction rule question regarding Sally’s car paint and speakers) would predict performance on its matched JDM problem in our study. The evidence is strongly in favor of this assertion - specific knowledge predicts better performance on matching JDM questions across a range of specifications.

Inferential rules as a moderator of individual differences

The prior section examined the main effect of access to inferential rules on task performance. In Question 5 we also asked whether particular individual differences would be more beneficial to task performance for participants who had better access to inferential rules. Multiple tests suggested that this was the case. In Models 11–13 (Table 5) we observed significant positive interactions between Rule _Specific and CRT (b = 0.087; p < 0.001), Rule _Specific and CRT-2 (b = 0.064; p = 0.008), and Rule _Specific and BNT (b = 0.157; p < 0.001). These interactions were robust to the inclusion of interaction terms between the individual difference measures and the Rule _Non-specific variable (Models 11a-13a; Table S9). We did not include all three Rule- _Specific X Individual Difference interactions at the same time due to collinearity concerns. In another robustness check, we included the variable Rule _Total (a participant’s score out of 12 for all rule questions answered correctly), as well as our Rule _Specific variable in our analyses. When including this Rule _Total variable, the main effect of Rule _Specific and its interactions with our individual difference measures remained statistically significant (Table S10). This shows further evidence that problem-specific rules have predictive power for decision making accuracy over and above a general measure of statistical knowledge.³

To illustrate these interactions, Figure 2 plots the proportion of correct responses to JDM questions across scores on the individual difference measures (the X-axis in each plot) and performance on the Rule _Specific variable broken out as separate lines to reflect each level of the Rule _Specific score (0, 1, or 2). The raw data (which includes 12 observations per participant) illustrate the same pattern found in the logistic regression models. Access to the rule yielded a larger benefit among those high in CRT, CRT-2, or BNT than among those low in these abilities. The fanning interactions illustrate that more reflective cognitive dispositions confer a greater boost to those who have access to the rule than those who do not (Kahneman, 2000; Nisbett, 1993; Toplak, West & Stanovich, 2011).

Figure 2: Proportion of correct responses on JDM questions by Rule_Specific score and score on individual difference measures. Note. Each panel looks at the proportion of correct responses across the levels of a different individual difference measure (CRT, CRT-2, BNT) at each level of Rule _Specific (0, 1, 2 – indicated by the shape that plots the line).

Inferential rules as a moderator of behavioral interventions

In order to understand the moderating effect of access to the relevant inferential rule on the impact of our behavioral interventions, we first interacted the variable Rule _Specific with our interventions, using Fast as the omitted condition. As shown in Model 8 (Table 4), the interactions were suggestive, although none of them reached the pre-determined threshold for significance of α = 0.05. The interaction between Rule _Specific and control (b = 0.142; p = 0.082) came close to achieving significance, but the interaction between the Rule _Specific and Slow was not significant (b = 0.138; p = 0.175). In Table S2, estimates for these interactions can be found when also interacting our conditions with the Rule _Non-specific variable. None of these were significant, although the interaction with control again came close.

Our primary analyses concern the effects of our interventions relative to a control condition. In Question 6a and Question 6b we asked whether participants who had access to the relevant rule would be particularly helped in the Slow condition and particularly harmed in the Fast condition, relative to a control. In Table 5 (Model 10), we see that there was no evidence of a positive interaction between Slow and Rule _Specific (b = −0.004; p = 0.959). However, we found some evidence for the effects of our Fast manipulation being more harmful to those who had access to the relevant inferential rule (b = −0.142; p = 0.082). When including the interaction between Fast and Rule _Non-specific (Model 10a, Table S9), the magnitude of this effect was slightly reduced (b = −0.123; p = 0.138).

To follow up on this, we re-ran the model with condition coded as either Fast or Not Fast. In principle this could increase power, because Fast is being compared to all the other conditions as opposed to the control alone. Although the test was formally inconclusive, the Fast X Rule _Specific interaction again indicated that being sped up may be particularly harmful for those who have access to the relevant inferential rule (b = −0.150; p = 0.051; Model 8b; Table S2).

In a different approach, when using linear regression to predict the total number of questions answered correctly, there is a significant negative interaction between the number of Rule questions answered correctly (Rule _Total) and our Fast manipulation (Model 3, Table S11; b = -0.126, p = 0.014). However, this methodology loses the specificity of matching Rule measures to corresponding problems.

On the whole, these results provide some evidence that when cognitive processes are impaired by a fast thinking manipulation, performance is hurt, particularly if one has access to the relevant inferential rule. We stress the need for caution in interpreting this interaction – while floor or ceiling effects are not likely (average accuracy across the between-subjects conditions was 58.5%), this interaction was sensitive to what variables were included in the regression equation. We find no support for the notion that, relative to a control, our Slow intervention worked better for those who had access to the relevant inferential rule. This stands in contrast to the interactions we found between our individual difference measures and Rule _Specific as described in the previous section. For example, those high in CRT had a greater benefit to response accuracy from higher levels of rule accessibility than the benefit to those who were low in CRT.

Incentives for accuracy.

Including an incentive condition in our study design enabled us to compare how participants performed when the stakes were raised relative to our other conditions. In Figure 1 (Panel B) we see that participants in the Incentive condition had about 8 percentage points higher average accuracy relative to participants in the Fast condition, but only about 2 percentage points better accuracy than participants in the control condition. Measured relative to our control, the effect of our Incentive condition did not attain statistical significance across models 1–5 (Table 2). (In Table 5, we estimated regression models including our Rule variables, and found a positive effect of Incentive (b = 0.148; p = 0.023; Model 9).

The answer to Question 7 is mixed. Overall, incentives yielded a significant benefit relative to the Fast condition, but a small benefit relative to the control, and its significance depended on model specification (in this case, the inclusion of the Rule variables).

One reason why incentives may be ineffective relative to the control condition is that participants do not possess the cognitive capital to improve their problem performance (Camerer & Hogarth, 1999). In Table 5, we looked at the interactions between our manipulations relative to our control condition and access to inferential rules. None attained statistical significance. The interaction between Rule _specific and the Incentive condition (b = 0.046, p = 0.575; Model 10) did not come close to significance.

Overall, we do not see large effects of incentives or slow thinking, and their significance is dependent on model specification. Given that the magnitude of the two was similar, however, encouraging slow thinking might be a more cost-effective alternative for improving performance than offering incentives.

Comparing between- and within-subjects tests of fast thinking and slow thinking

Previous research has examined fast thinking vs slow thinking using a within-subjects design in which respondents provided two responses in succession: An initial ‘intuitive’ answer and a final answer after reflection (Bago & De Neys, 2017). Our design allowed us to compare the esults derived from this within-subjects framework with our between-subjects design. Importantly, the two-response paradigm elicited the expected performance differences between the two responses: Participants achieved 50.7% accuracy in the Fast _within response and 59.1% accuracy in the subsequent Slow _within response.

To analyze the within-subjects responses, we split each participant’s responses into their first (Fast _within) and final (Slow _within) responses, and used them in separate models that each performed between-subjects tests. We estimated two logistic regression models using our GEE procedure, including either the Fast _within or the Slow _within responses from the within-subject condition, along with the full sample of our between-subjects design that included the corresponding intervention conditions analyzed earlier (which we label Fast _between and Slow _between in this section to minimize confusion). Models 14 and 15 can be seen in Table 6. Both models use the control condition as the omitted category for testing the intervention dummy variables.

Table 6: Logistic regressions predicting success with conditions coded relative to control and with individual differences mean centered, including half of the within-subjects observations.

Note.

^*** p < 0.001

^** p < 0.01

^* p < 0.05

^† p < 0.10

The coefficient estimates for Measure, Problem, Position, and Block Order effects are included in the supplement (Table S12).

The traditional critique of the two-response paradigm suggests that the initial Fast _within response will impede successful reasoning in the second, Slow _within response. We do not find support for this critique of the two-response paradigm: Participants’ Slow _within responses were not significantly worse than the control condition (b = −0.042; p = 0.580), consistent with other research (Bago & De Neys, 2019a). Our design also allows us to test a different concern: Do the Slow _within responses of the two-response paradigm achieve similar performance to the between-subject Slow _between condition? In Model 15, we show that although the Slow _between manipulation predicts better decision making relative to the control (b = 0.155; p = 0.049), the Slow _within condition (i.e. the second responses of participants in the two-response paradigm) is not close to being significantly better than the control condition.

Re-estimating Model 15 using the Slow _within condition as the omitted category (Table S12; Model 15a) reveals that subjects’ answers in the Slow _between condition were significantly more accurate than those in the Slow _within condition (b = 0.197; p = 0.037). However, when we include Rule _Specific and Rule _Non-specific in a regression equation performing this test, the difference shrinks and no longer attains statistical significance (b = 0.165; p = 0.061). This could be due to participants performing slightly better on our Rule items in the Slow _between condition (M = 9.50) relative to our Slow _within condition (M = 9.43). Consequently, we emphasize the need for caution in interpreting these results. It seems that after accounting for the effect of Rule scores, our between-subjects Slow condition performs slightly better than our within-subjects Slow responses, but neither Slow condition differs significantly from the control.

4 General Discussion

Previous research has not regularly simultaneously compared fast thinking and slow thinking to a control group. The current research suggests that fast thinking is indeed harmful to the accuracy of statistical judgments, but the benefits of slow thinking are smaller. Speeding people up and asking them to make an intuitive judgment hurts performance, replicating previous findings (Evans & Curtis-Holmes, 2005; Villejoubert, 2009). In contrast, an intervention to encourage slow thinking had a beneficial effect relative to the control, but this appears to be at least partly a result of random variation in rule scores across conditions. When accounting for the effects of rules, there was no significant benefit of slow thinking relative to a control, but still a benefit of slow thinking relative to fast thinking. The present research provides initial evidence that, compared to a baseline control group, encouraging slow thinking has limited benefits for canonical, statistical JDM problems.

We replicate past work by finding large and reliable effects of individual differences on JDM problem performance (Frederick, 2005; Oeschssler et al., 2009; Koehler & James, 2010). Individual difference effects, as often studied in past work, are useful standards against which to compare the benefits of interventions. We find that inducing subjects to switch from fast to slow thinking has the same sized benefit as improving a decision maker’s score by 1 point on the 4-point CRT scale. This difference is driven more by the harm of fast thinking than by the benefit of slow thinking (compared to a control group).

We find support for the theoretical importance of rules (Nisbett, 1993) as a component of dual-system frameworks (Kahneman, 2000; Sloman, 1996). We measure participants’ performance in simple statistical problems to ascertain whether individuals have access to the knowledge relevant to a focal JDM task. People’s ability to use this knowledge in easier problems predicts their success at applying it to harder problems that invite competing intuitive responses. Notably, we find that performance in matched rule questions (questions that measure access to the specific rule underpinning the focal problem) appears to be more predictive of problem success than performance in other rule questions. Our variable Rule _Specific was predictive of task success when including individual difference measures (CRT, CRT-2, BNT) and access to other, non-specific rules in our regression formulae. Accuracy in answering JDM questions in our control condition improved by 42 percentage points across levels of the Rule _Specific measure (from 0 to 2), a magnitude comparable to improvement observed across the range of CRT (0 to 3). This effect is larger than that observed with a 2-point improvement on a different rule question of 30.7 percentage points. Taken together, our results show that there is a larger benefit to rule-specific knowledge than that conferred by knowledge of statistical rules in general.

We also find suggestive evidence that speeding people up is particularly damaging when decision makers have access to the relevant inferential rule – having to engage in fast thinking appears to disrupt access to and the ability to apply relevant knowledge. In sum, our results suggest that both the knowledge one has access to and one’s approach to reasoning affect accuracy in solving JDM statistical problems.

These results raise the possibility of trying to provide people with simple rules for reasoning through training and education (Fong & Nisbett, 1991; Nisbett, 1993). Alas, training is costly and daunting. How and when would such interventions occur? The field of JDM has focused on external interventions (nudges, such as defaults) because they build on individual cognitive tendencies rather than attempt to change them. As technology makes gamification a powerful (and fun) tool, it may be possible to use rich and engaging feedback environments as tools for imparting the most important knowledge (Hogarth & Soyer, 2011, 2015). Several research teams have shown the benefit of using brief, immersive training techniques for learning to avoid biases (e.g., such as confirmation bias) (Morewedge et al. 2015; Sellier, Scopelliti & Morewedge, 2019; Mohan et al., 2017; Mohan et al., 2018). Similar techniques could be used to teach statistical principles such as the law of large numbers and the need to consider four cells when judging covariation.

The early theorizing about System 2 emphasized the joint contribution of rules and decision processes (Kahneman, 2000; Sloman, 1996). More recent work on System 2 has focused more on process (slow thinking and reflection) than on access to rules. The current research supports the merits of the earlier focus on their joint contribution. Having access to the necessary inferential rule to reach the normative answer in a problem is important, as is having cognitive faculties that are relevant to problem solving. Significant interactions show that scoring higher on the Berlin Numeracy Test (Cokely et al., 2012) or being more dispositionally reflective (as measured by CRT and CRT-2) are each more beneficial to performance for people who have access to the relevant inferential rules. This finding is in line with the claim that avoiding decision biases requires both having the right decision strategy and recognizing when to use it (Kahneman, 2000; Nisbett, 1993).

Finally, we compared the benefits of fast thinking and slow thinking using two different popular paradigms, one comparing them between-subjects (e.g., Evans, Handley & Bacon, 2009; Cryder et al., 2017) and the other using a sequential paradigm within-subjects (e.g., Thompson et al., 2011; Bago & De Neys, 2017). We do not find evidence supporting an anchoring critique of the two-response paradigm – participants in the within-subjects Slow condition performed no worse than the control group. However, they also did not perform better than the control condition. As a result, it appears that there was a small benefit of the between-subjects Slow intervention (61.6%) beyond the performance achieved by the slow thinking responses from the within-subjects condition (59.1%), although this lost statistical significance when rules were included in the models.

4.1 Limitations

A potential critique of the asymmetry between the cost of fast thinking and the benefit of slow thinking observed in the present research is that some people may not fully comply with the instructions. Specifically, fast and slow instructions may evoke different rates of compliance – it takes less effort to be fast than to be slow. Thus, the slow instructions may be rejected by some participants, reducing the overall performance of the group of subjects in that condition. We believe that there are at least three reasons why the asymmetry between the effects of fast and slow thinking interventions is likely to persist in different contexts. First, our robustness checks, although not perfect, continued to show the asymmetry even when the data were trimmed to exclude participants who might not have fully complied (Table S4). Second, our findings mostly mirror recent research on incentives showing that very high pay for correct answers can cause people to slow down without leading to improved performance (Enke et al., 2020). Thus, our experiment complements other work showing a weak association between deliberately taking more time and accuracy on JDM tasks. Finally, even if slow thinking does help those who take it seriously, mere instruction to think more slowly apparently produces lackluster adoption – a problem that would likely persist in settings outside experiments, such as classrooms and workplaces. The underwhelming effects of slow thinking in our data could be driven by failure to fully comply, among other factors. Regardless of the underlying mechanism, the result is an important one from a debiasing perspective. The JDM field should have realistic expectations of the benefit of telling people to think more slowly on statistical reasoning as captured by the problems of traditional interest to the field.

It is also possible that if participants slowed down even more, there might be performance gains that we do not observe here. As we see in Table 3, telling people to think more slowly slows them down about 20% relative to a control. This is insufficient to produce a consistent performance advantage. Perhaps slowing down more would be beneficial, but there are at least two reasons to be skeptical. First, research has shown that forcing people to slow down beyond what is natural can harm performance (Payne et al., 2008). Second, even when very large incentives cause participants to slow down a great deal (40% longer response times, as in Enke et al., 2020), there are still negligible impacts on performance in classic JDM tasks. From the available evidence, we conclude that it is unlikely that there are significant benefits associated with slow thinking in statistical JDM problems that can be attained by slowing down further.

Our results generally support the idea that encouraging slow thinking has limited benefits relative to a control condition in an experiment. However, further attention to the relevant baseline is necessary. Our JDM questions were difficult, and the context of the experiment is likely to have induced slower thinking than participants might exhibit in everyday situations. If, in real world settings, decision makers are likely to be engaging in split second decisions, a simple prompt to slow down may be of use. In domains that seem to foster fast thinking, such as social media, research has found that a simple encouragement to slow down can have significant benefits in detecting fake news (Pennycook, McPhetres, Zhang, Lu & Rand, 2020). Our results cannot attest to the benefits of slow thinking in other contexts, but we can suggest that differences in performance between fast and slow thinking in statistical decision making studies in the laboratory are likely to be driven more by the harm of fast thinking than the benefit of slow thinking when compared to participants’ baseline tendencies.

4.2 Conclusion

In the wake of Daniel Kahneman’s (2011) Thinking, Fast and Slow, popular rhetoric has emphasized the benefits of slow thinking. Yet recent academic research into dual process theory has produced a dearth of evidence supporting the idea that choosing to slow down has a benefit to decision quality relative to individuals’ baseline. Bodies of evidence show that more habitually reflective thinkers avoid many common decision biases and that slow thinking is generally superior to fast thinking. Direct evidence concerning the benefits of slowing down as a debiasing strategy has been lacking. In the present research, we directly test the benefits of slow thinking versus a control, and draw on the literature on inferential rules for a possible moderator of when slowing down is likely to be helpful. Whilst we do not find strong evidence supporting the benefits of slow thinking, our results reinforce the importance of considering inferential rules in a dual process framework, in line with Sloman’s (1996) original formulation. We hope that the current research is seen as a bridge between assertions adopted in popular interpretations of JDM research and the extant empirical evidence.

Even though the effect of our thinking slow manipulation is small and not reliably significant, this still constitutes a readily implemented behavioral intervention. In problems where people do habitually engage in split-second thinking, a simple encouragement to think more slowly might be beneficial to achieving superior performance. In our data, the benefit of slow thinking was comparable in size to offering an incentive for performance. For our JDM problems, briefly guiding decision makers to a slow process is as effective as focusing their attention on accuracy rewards. The prescription to think slowly is at least more cost-effective. Further research might examine if there are other contexts in which a simple instruction to slow down can more clearly improve task performance.