Adam Ozimek reads a year-old paper (pdf) on the subject:
Among the many interesting results they report are that 40% of prostitutes have a college degree, and 80% have had some college. Apparently, the current economic downturn has led to churn in the industry and lower wages, as supply has expanded and demand has contracted. For many women this puts the market wage below their reservation wage, which drives them out of the market.
2006-2011 archives for The Daily Dish, featuring Andrew Sullivan