de la Cuesta, Brandon and Kosuke Imai. (2016). ``Misunderstandings about the Regression Discontinuity Design in the Study of Close Elections.'' Annual Review of Political Science, Vol. 19, pp. 375-396.



Recently, the regression discontinuity (RD) design has become increasingly popular among social scientists. One prominent application is the study of close elections. We explicate several methodological misunderstandings widespread across disciplines by revisiting the controversy concerning the validity of RD design when applied to close elections. While many researchers invoke the local randomization or ``as-if-random'' assumption near the threshold, it tends to be more stringent than the required continuity assumption. We show that this seemingly subtle point determines the appropriateness of various statistical methods and changes our understanding of how ``sorting'' invalidates the design. When multiple testing problems are also addressed, we find that evidence for sorting in US House elections is substantially weaker and highly dependent on estimation methods. Finally, we caution that despite the temptation to improve the external validity, the extrapolation of RD estimates away from the threshold sacrifices the design's advantage in internal validity.

© Kosuke Imai
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