In 1980 the state of Rhode Island made a change to its laws prohibiting the exchange of sex for money. No one paid much attention until 2003 when a very observant lawyer helped massage parlor workers beat prostitution charges by pointing out that an unintended loophole made it legal to sell, or buy, sexual services provided this occurred indoors.
Commercial sex is illegal in 49 of America's 50 states (unless performed for film) and heavily restricted in Nevada. Rhode Island legislators hadn't planned to change that, and quickly decided to change back. However, the part-time state legislature took until 2009 to work out exactly how to revise their decision, and for that time indoor commercial sex between consenting adults carried no legal penalty.
For Baylor University's Dr Scott Cunningham and UCLA's Dr Manisha Shah, this period represented a perfect natural experiment to strip away a lot of the guesswork that usually dominates debate on this exceptionally contentious issue. In the Review of Economic Studies, the two compare what happened in Rhode Island during the six years of decriminalization to the situation in the rest of the United States.
Although it is hard to get data on the size of the sex industry, particularly when it's illegal, Cunningham and Shah found evidence for more advertising of indoor sex sales, and a 33 percent fall in prices, leading to a larger market. They also reveal dramatic falls during this period in sexually transmitted diseases and reported rape across the whole community.
Gonorrhea rates among women in Rhode Island fell 40 percent between 2003-2009 and 25 percent among men, probably because of increased condom use. Lower STIs were expected since condom use is easier to negotiate in a secure environment. Moreover, US police forces often use possession of multiple condoms as evidence a suspect is a sex worker, making it dangerous to carry them. This is one of the reasons organizations tackling diseases like HIV usually support decriminalization. Any reduced transmission of an infectious disease tends to limit the spread through the community as a whole, but getting a reduction this large is the sort of change epidemiologists dream of, and it wasn't expected.
As the authors admit, the fall in reported rapes is harder to explain. Decriminalization is often argued to reduce assaults on sex workers since it is easier to report to police when not engaged in a criminal activity yourself. Nevertheless, the 30 percent reduction Cunningham and Shah recorded, taking the state from well above the national average to well below, occurred across the entire community, and their explanations are fairly tentative.