Evaluating Causal Relationships

Abstract

OVERVIEW Modern political science fundamentally revolves around establishing whether there are causal relationships between important concepts. This is rarely straightforward, and serves as the basis for almost all scientific controversies. How do we know, for example, if economic development causes democratization, or if democratization causes economic development, or both, or neither? To speak more generally, if we wish to evaluate whether or not some X causes some Y , we need to cross four causal hurdles: (1) Is there a credible causal mechanism that connects X to Y ? (2) Can we eliminate the possibility that Y causes X ? (3) Is there covariation between X and Y ? (4) Have we controlled for all confounding variables Z that might make the association between X and Y spurious? Many people, especially those in the media, make the mistake that crossing just the third causal hurdle – observing that X and Y covary – is tantamount to crossing all four. In short, finding a relationship is not the same as finding a causal relationship, and causality is what we care about as political scientists. I would rather discover one causal law than be King of Persia. – Democritus (quoted in Pearl 2000) CAUSALITY AND EVERYDAY LANGUAGE Like that of most sciences, the discipline of political science fundamentally revolves around evaluating causal claims. Our theories – which may be right or may be wrong – typically specify that some independent variable causes some dependent variable.