Steven Levitt & Sudhir Venkatesh, “An Empirical Analysis of Street-Level Prostitution” (Sept 2007 draft) 
This is a Levitt (of Freakonomics fame) paper.
http://economics.uchicago.edu/pdf/Prostitution%205.pdf

This is a Levitt (of Freakonomics fame) paper.
http://economics.uchicago.edu/pdf/Prostitution%205.pdf