HANDBOOK OF LABOR ECONOMICS, VOL 4A

4 Research Designs Dominated by Self-Selection

In this section, we briefly consider a group of research designs where institutional knowledge of the treatment assignment process typically does not provide most of the information needed to draw causal inferences. In Section 3, we discussed how some aspects of the assignment process could be treated more as literal “descriptions” (“D”-conditions), rather than conjectures or assumptions. In each of the four research designs, those “D” conditions went a long way towards identification, and when other structural assumptions (“S”-conditions) were needed, the class of models consistent with those assumptions, while strictly smaller because of the restrictions, arguably remained very broad.

With the ...