In a post on the New York Times Economix blog, Casey Mulligan claims that the federal minimum wage increase on July 24, 2009 caused a loss of part-time jobs. To support this, he uses nationwide data showing a significant slow-down in the growth of part-time jobs just after the 2009 minimum wage increase. (Interestingly, his data also show, although he does not point this out, that the previous federal minimum wage increase on July 24, 2008 had no impact whatsoever on part-time jobs.)

Mulligan’s simple exercise is deeply flawed: the summer of 2009, when the wage increase occurred, was a period of significant economic turmoil, and job losses averaged 350,000 per month from June to August. His simple pre- and post-enactment analysis will not separate the impact of the minimum wage increase from the many other changes in the economy over that time period.