Why are white women dropping out of the job market?

The unemployment rate fell to a three-year low of 8.2% in March, but it wasn't because more Americans found jobs. Instead, thousands of people dropped out of the labor market.

Who were those people?

White women, mainly.

Roughly 136,000 white women left the labor force in March. Their participation in the job market has been slowly dropping since mid 2009, and now it's at levels not seen since 1996.

In contrast, white men have also recently left the labor force, but not nearly as dramatically in March. And blacks of both genders have been wading back into the job market. (The Labor Department doesn't collect seasonally adjusted data on Hispanics and Asians).

Why are white women leaving? Unfortunately, it's impossible to tell from the Labor Department's data. Reasons could include going back to school, retiring, staying home to take care of family or having a disability.

Or perhaps they're just giving up on the job market altogether.