Comment

Chemin and Wasmer attempt the first evaluation, to my knowledge, of French labor market interventions using the technique known as regional difference-in-differences, first popularized in labor economics by Ashenfelter (1978) and now one of theworkhorses of empirical labor economics. Their paper uses regional variation in labor market institutions, long thought to be nonexistent in France, to make a first pass at evaluating three interventions: the 1989welfare law that established aminimum income for individuals above age 25 regardless of employment status (RevenuMinimum d’Insertion), the 1978 changes to the national sick leave policy (indemnisation complémentaire), and the 1998–2000 phase-in of the French 35-hour workweek (réduction du temps de travail). My discussion will focus on the last of these experiments because it was the one that motivated the present paper and because the authors' other work indicates that they have studied this intervention more carefully than the first two. In each case, the preliminary evaluation, which is all they provide in this paper, makes use of institutional differences in the Alsace-Moselle region of France (technically a political region, Alsace, and a political département, Moselle). This region has been (infamously) disputed between France and Germany and was last subject to German national law from 1870 to 1918. As a vestige of this era, the political entities (départements) within Alsace-Moselle retain as local law some of the original German laws. Essentially, whenever the historical German laws were more generous than the prevailing French national laws, the AlsaceMoselle region was permitted to retain the more generous provisions. This regional variation provides the setting for the authors’ differencein-difference evaluation of the three interventions. As French national laws became more generous over time, they created changes in the rest of the country that did not occur as sharply in Alsace-Moselle because in that region the applicable laws were already more generous.