Punctuated equilibrium or incrementalism in policymaking: What we can and cannot learn from the distribution of policy changes

Theories in political science are most commonly tested through comparisons of means via difference tests or regression, but some theoretical frameworks offer implications regarding other distributional features. I consider the literature on models of policy change, and their implications for the thickness of the tails in the distribution of policy change. Change in public policy output is commonly characterized by periods of stasis that are punctuated by dramatic change—a heavy-tailed distribution of policy change. Heavy-tailed policy change is used to differentiate between the incrementalism and punctuated equilibrium models of policy change. The evidentiary value of heavy-tailed outputs rests on the assumption that changes in inputs are normally distributed. I show that, in order for conventional assumptions to imply normally distributed inputs, variance in the within-time distribution of inputs must be assumed to be constant over time. I present this result, and then present an empirical example of a possible aggregate policy input—a major public opinion survey item—that exhibits over-time variation in within-time variance. I conclude that the results I present should serve as motivation for those interested in testing the implications of punctuated equilibrium theory to adopt more flexible assumptions regarding, and endeavor to measure, policy inputs.