freakonomics
n. funky study of supply, demand and incentives
Freakonomics is the study of economics from a contrarian perspective, ie with the willingness to turn conventional wisdom on its head. Freakonomists amass a large amount of data to answer simple but funky questions, such as: "Given that most drug dealers live with their mothers, does selling crack really bring in more income than working at McDonald’s?" (via The Observer).
The other example that is largely quoted is the link between the legalisation of abortion in the 1970s and the fall of crime in the 1990s in the USA. In general, women who seek an abortion are in a situation that makes it very difficult or impossible for them to raise a child (financial difficulties, vulnerable situation, young age, etc.), and their children are therefore more likely to become criminals when they reach adulthood. This is how, according to freakonomics, the legalisation of abortion has led to a reduction in the number of criminals in the 90s.
For more details, see Steven D. Levitt and Stephen J. Dubner’s site.