A common approach when studying the quality of representation involves comparing the latent preferences of voters and legislators, commonly obtained by fitting an item response theory (IRT) model to a common set of stimuli. Despite being exposed to the same stimuli, voters and legislators may not share a common understanding of how these stimuli map onto their latent preferences, leading to differential item functioning (DIF) and incomparability of estimates. We explore the presence of DIF and incomparability of latent preferences obtained through IRT models by reanalyzing an influential survey dataset, where survey respondents expressed their preferences on roll call votes that U.S. legislators had previously voted on. To do so, we propose defining a Dirichlet process prior over item response functions in standard IRT models. In contrast to typical multistep approaches to detecting DIF, our strategy allows researchers to fit a single model, automatically identifying incomparable subgroups with different mappings from latent traits onto observed responses. We find that although there is a group of voters whose estimated positions can be safely compared to those of legislators, a sizeable share of surveyed voters understand stimuli in fundamentally different ways. Ignoring these issues can lead to incorrect conclusions about the quality of representation.

Predictors used to calculate the body mass of extinct carnivorans often scale differently between different taxa, thus yielding body mass estimates that diverge considerably depending on which predictive equation is used. This requires the investigator to choose the ones most suitable, a procedure that is best avoided if possible. The carnivoran elbow joint is here explored with the aim of producing a single general body mass predictor that can be used over a broad range of terrestrial and arboreal carnivorans. The circumference of the distal humerus trochlea is found to be highly correlated with body mass, and trochlea circumference seems to scale similarly throughout the order Carnivora. This scaling is not as theoretically predicted by elastic similarity and is slightly higher than that predicted by geometric similarity, indicating a slight positive allometry for the latter. Some degree of differential scaling between carnivoran families and between animals of large and small size cannot be ruled out, but this result is inconclusive. A predictive model that allows mass estimations for a broad range of carnivorans is presented (a=0.601; b=2.552; r2=0.952, SEE=0.136, P<0001, n=92). Body mass for eight extinct carnivoran species are calculated and these generally conform to earlier mass predictions.