たぶん、実証的にはそんなにはっきりと言い切れないと思いますが。ド素人ですが、私めがミクロ計量の授業で聞いたところによると、Difference in Differenceを用いた以下の有名な論文以降、いろいろと論争があるらしいです。
David Card, Alan B. Krueger
Minimum Wages and Employment: A Case Study of the Fast-Food Industry in New Jersey and Pennsylvania
On April 1, 1992, New Jersey's minimum wage rose from $4.25 to $5.05 per hour. To evaluate the impact of the law, the authors surveyed 410 fast-food restaurants in New Jersey and eastern Pennsylvania before and after the rise. Comparisons of employment growth at stores in New Jersey and Pennsylvania (where the minimum wage was constant) provide simple estimates of the effect of the higher minimum wage. The authors also compare employment changes at stores in New Jersey that were initially paying high wages (above $5.00) to the changes at lower-wage stores. They find no indication that the rise in the minimum wage reduced employment. Copyright 1994 by American Economic Association.
David Card, Alan B. Krueger
Minimum Wages and Employment: A Case Study of the Fast-Food Industry in New Jersey and Pennsylvania: Reply
After analyzing BNW’s data, our original survey data, publicly available BLS data, and most importantly, the BLS ES-202 fast-food establishment data, we reach the following conclusion: The increase in New Jersey’s minimum wage probably had no effect on total employment in New Jersey’s fast-food industry, and possibly had a small positive effect. We have previously written that, because of frictions in the labor market, a minimum wage increase can be expected to cause some firms to reduce employment and others to raise employment, with these two effects potentially cancelling out if the rise in the minimum wage is modest (Card and Krueger, 1995 especially pp. 13–14). If this view is correct, then it would not be surprising to find some specifications and data definitions that yield a negative impact of the minimum wage on employment. But we doubt that a representative survey of fast-food restaurants in New Jersey and eastern Pennsylvania would show a significant adverse impact of the minimum wage on total employment.
The only data set that indicates a significant decline in employment in New Jersey relative to Pennsylvania is the small set of restaurants collected by EPI. Results of this data set stand in contrast to our survey data, to the BLS’s payroll data, and to the supplemental data collected by Neumark and Wascher. The difference between the New Jersey-Pennsylvania comparison in our original survey and BNW’s data cannot be reconciled by inherent differences between a telephone survey and administrative payroll records because the BLS ES-202 data are based on administrative payroll records. Instead, we suspect the common denominator is that representative samples show statistically insignificant and small differences in employment growth between New Jersey and eastern Pennsylvania, while the nonrepresentative sample informally collected for Berman produces anomalous results.
An alternative interpretation of the full spectrum of results is that the New Jersey minimum wage increase did not reduce total employment, but it did slightly reduce the average number of hours worked per employee. Neumark and Wascher (1995b) reject this interpretation. Although we are less quick to rule out this possibility, we are skeptical about any conclusion concerning average hours worked per employee that relies so heavily on the informally collected Berman/EPI sample, and the exclusion of controls for the length of the reporting interval. Moreover, within New Jersey the BNW data indicate that hours grew more at restaurants in the lowest wage areas of the state, where the minimum-wage increase was more likely to be a binding constraint. This finding runs counter to the view that total hours declined in response to the New Jersey minimum wage increase.