A search of recent political science literature and conference presentations shows substantial fascination with the concept of the natural experiment. However, there seems to be a wide array of definitions and applications employed in research that purports to analyze natural experiments. In this introductory essay to the special issue, we attempt to define natural experiments and discuss related issues of research design. In addition, we briefly explore the basic methodological issues around the appropriate analysis of natural experiments and give an overview of different techniques. The overarching theme of this essay and of this issue is to encourage applied researchers to look for natural experiments in their own work and to think more systematically about research design.

Although there are compelling theoretical reasons to believe that unequal political representation in a legislature leads to an unequal distribution of funds, testing such theories empirically is challenging because it is difficult to separate the effects of representation from the effects of either population levels or changes. We leverage the natural experiment generated by infrequent and discrete census apportionment cycles to estimate the distributional effects of malapportionment in the U.S. House of Representatives. We find that changes in representation cause changes in the distribution of federal outlays to the states. Our method is exportable to any democratic system in which reapportionments are regular, infrequent, and nonstrategic.

In this case study of the impact of West German television on public support for the East German communist regime, we evaluate the conventional wisdom in the democratization literature that foreign mass media undermine authoritarian rule. We exploit formerly classified survey data and a natural experiment to identify the effect of foreign media exposure using instrumental variable estimators. Contrary to conventional wisdom, East Germans exposed to West German television were more satisfied with life in East Germany and more supportive of the East German regime. To explain this surprising finding, we show that East Germans used West German television primarily as a source of entertainment. Behavioral data on regional patterns in exit visa applications and archival evidence on the reaction of the East German regime to the availability of West German television corroborate this result.

Regression discontinuity (RD) designs enable researchers to estimate causal effects using observational data. These causal effects are identified at the point of discontinuity that distinguishes those observations that do or do not receive the treatment. One challenge in applying RD in practice is that data may be sparse in the immediate vicinity of the discontinuity. Expanding the analysis to observations outside this immediate vicinity may improve the statistical precision with which treatment effects are estimated, but including more distant observations also increases the risk of bias. Model specification is another source of uncertainty; as the bandwidth around the cutoff point expands, linear approximations may break down, requiring more flexible functional forms. Using data from a large randomized experiment conducted by Gerber, Green, and Larimer (2008), this study attempts to recover an experimental benchmark using RD and assesses the uncertainty introduced by various aspects of model and bandwidth selection. More generally, we demonstrate how experimental benchmarks can be used to gauge and improve the reliability of RD analyses.

Although the presidential coattail effect has been an object of frequent study, the question of whether popular congressional candidates boost vote shares in return for their parties' presidential candidates remains unexplored. This article investigates whether so-called “reverse coattails” exist using a regression discontinuity design with congressional district-level data from presidential elections between 1952 and 2004. Taking incumbency to be near-randomly distributed in cases where congressional candidates have just won or lost their previous elections, I find that the numerous substantial advantages of congressional incumbency have no effect on presidential returns for these incumbents' parties. This null finding underscores my claim that the existing coattail literature deserves greater scrutiny. My results also prompt a rethinking of the nature of the advantages that incumbents bring to their campaigns and may help deepen our understanding of partisanship in the United States.

The consolidation of polling places in the Vestal Central School District in New York State during the district's 2006 budget referendum provides a naturalistic setting to study the effects of polling consolidation on voter turnout on an electorate quite distinct from previous work by Brady and McNulty (2004, The costs of voting: Evidence from a natural experiment. Presented at the Annual Meeting of the Society for Political Methodology, Palo Alto, CA). In particular, voters in local elections are highly motivated and therefore might be thought to be less affected by poll consolidation. Nevertheless, through a matching analysis we find that polling consolidation decreases voter turnout substantially, by about seven percentage points, even among this electorate, suggesting that even habitual voters can be dissuaded from going to the polls. This finding has implications for how election administrators ought to handle cost-cutting measures like consolidation.