the delicate balance between these factors helps explain why, for instance, the typical prostitute earns more than the typical architect. it may not seem as though she should. the architect would appear to be more skilled (as the word is usually defined) and better educated (again, as usually defined). but little girls dont grow up dreaming of becoming prostitutes, so the supply of potential prostitutes is relatively small. their skills, while not necessarily "specialised", are practiced in a very specialised context. the job is unpleasant and forbidding in at least two significant ways: the likelihood of violence and the lost opportunity of having a stable family life. as for demand? let's just say an architect is more likely to hire a prostitute than vice versa.

-- freakanomics