The Necessity of Construct and External Validity for Generalized Causal Claims∗ Kevin M. Esterling David Brady (Corresponding Author) Professor Professor School of Public Policy School of Public Policy and UC{Riverside and Department of Political Science WZB Berlin Social Science Center UC{Riverside
[email protected] [email protected] Eric Schwitzgebel Professor Department of Philosophy UC{Riverside
[email protected] June 18, 2021 ∗An earlier version was presented as part of the WZB Talks series. We thank Elias Barein- boim, Michael Bates, Shaun Bowler, Nancy Cartwright, Carlos Cinelli, Uljana Feest, Diogo Ferrari, Christian Fong, Francesco Guala, Steffen Huck, Macartan Humphreys, Robert Kaest- ner, Sampada KC, Jon Krosnick, Dorothea Kubler, Doug Lauen, Joscha Legewie, Michael Neblo, J¨orgPeters, Alex Rosenberg, Heike Solga, Jacqueline Sullivan, Nicholas Weller, Bernhard Wes- sels, Ang Yu and the participants in the MAMA workshop in UCR Psychology for comments. Abstract By advancing causal identification, the credibility revolution has facilitated tremendous progress in political science. The ensuing emphasis on internal validity however has led to the neglect of construct and external validity. This article develops a framework we call causal specification. The framework formally demonstrates the joint necessity of in- ternal, construct and external validity for causal generalization. Indeed, the lack of any of the three types of validity undermines the credibility revolution's own goal to under- stand causality deductively. Without construct, one cannot accurately label the cause or outcome. Without external, one cannot understand the conditions enabling the cause to have an effect. Our framework clarifies the assumptions necessary for each of the three.