  In Historical Economics, Persistence studies document the persistence of some
historical phenomenon or leverage this persistence to identify causal
relationships of interest in the present. In this chapter, we analyze the
implications of allowing for heterogeneous treatment effects in these studies.
We delineate their common empirical structure, argue that heterogeneous
treatment effects are likely in their context, and propose minimal abstract
models that help interpret results and guide the development of empirical
strategies to uncover the mechanisms generating the effects.
