By 2009, the perfect storm had formed that might even make the minimum wage noticeable from an aggregate point of view:
- The equilibrium wage likely fell due to deflation (about -2.1% July 2008 - July 2009)
- The equilibrium wage likely fell due to an increased supply of part-time workers, such as persons fired from their full-time jobs. Supply increased at least 10 percent in the quantity dimension, which pushed down the equilibrium real wage roughly 3 percent
- The nominal federal minimum wage had gotten high thanks to two recent previous hikes
- The nominal federal minimum wage was hiked again another 11 percent (from $6.55 to 7.25 per hour).
Thus, by June 2009 the federal minimum probably already exceeded the equilibrium wage for a significant number of workers, especially those part time. For example, the BLS estimates that 2.3 million part-time workers were at or below the federal minimum in 2009 (BLS does not specify which month or months, but I presume March gets a lot of weight), as compared to 1.4 million a year earlier.
So let's say that 2 million workers were affected by the 11 percent hike on July 24, 2009. With a labor demand elasticity of -3 (that's what Cobb-Douglas would predict), the textbook theory says that a half a million part-time workers would lose their jobs (or fail to be hired) due to the July 24, 2009 hike (525,177 = [1-(6.55/7.25)^3]*2,000,000).
Interestingly, the national data do suggest that about 500,000 part-time jobs were lost.
Without this perfect storm, the minimum wage would not be something of interest to macroeconomists, but "just" to observers of low-skill labor markets. Conversely, don't expect to see aggregate effects of the minimum wage unless the storm is as perfect as this one.