In a groundbreaking study, researchers at Baylor and West Virginia universities have found evidence indicating that craigslist’s erotic services site may have prompted a 17 percent decrease in female homicides throughout the U.S., principally because sex workers were able to use the free advertising service to move into a safer indoor environments and screen clients more carefully. The erotic services site, launched in 2002, was shut down in 2010 after attorneys general from several states threatened to sue craigslist.

The study, which has been submitted to a peer-reviewed economics journal, offers the first solid evidence of what sex workers have been saying for years: that having the ability to advertise online for their services allows them to work in safer indoor environments and screen out violent clients. The new study reinforces previous research showing a decline in sexual violence in regions where prostitution has been legalized or decriminalized. I wrote about such research in my book, Getting Screwed; Sex Workers and the Law and in an op-ed piece for the Los Angeles Times.

It is well-known that illegal prostitution is a dangerous occupation with a high homicide rate (2.7 percent of all female homicides in the United States involve prostitutes.) Working outdoors is particularly hazardous, with street prostitutes experiencing a homicide rate over 13 times that of the general population. That’s because violent predators (including serial killers) are far more likely to prey on street walkers they can pick up in their cars than they are on indoor sex workers who have the ability to screen clients using online tools. Indeed, as the authors of this new study note, serial killers accounted for more than one-third of prostitute victims and nearly all such serial killers were clients.

The WVU and Baylor researchers found not only that female homicide rates declined by 17 percent during the time craigslist offered its free advertising services for sex workers nationwide. By analyzing thousands of client reviews posted on a popular website, The Erotic Review, they also discovered that a growing number of sex workers throughout the U.S. migrated indoors and were able to more carefully screen clients by using craigslist’s erotic review services. They conclude that this movement indoors and the more efficient use of online screening by sex workers is what led to the reduction of female homicides in the years craigslist site was operational:

We propose four mechanisms that could explain our results. First, the introduction of ERS may have caused outdoor street-based prostitution to transition to the safer, indoor channel…Second, the growth of the market, combined with more efficient matching may lead to repeat business with low-risk clients, thereby making the market lower risk to sellers. Third, ERS may have enabled more screening, such as the use of references when seeing new clients or background checks. And fourth, ERS may have led to greater deterrence of client violence through the creation of a digital fingerprint that made detection of criminal offenses more likely…We conclude that more efficient matching, growth in repeat business, and transitioning indoors are responsible for the decline in murders.

Interestingly enough, the researchers also did an analysis of how many more police officers would need to be hired to reduce the female homicide rate by the same percentage that craigslist’s free service apparently did. They concluded that this would require an additional outlay of 200,832 police officers, costing the U.S.an added $20 billion per year.

“Craigslist, in other words, saved 2,150 female lives at profoundly lower social cost,” concluded the three authors, Scott Cunningham, an economics professor at Baylor; Gregory DeAngelo, an economics professor at WVU; and John Tripp, an information systems professor at Baylor.

Here’s the rub: pressured by law enforcement, a number of online advertising sites for sex workers have recently been forced to shut down, including craigslist, Backpage, my redbook and The Review Board in Seattle. Yet as I have argued repeatedly in essays and blogs, this approach is only making life more dangerous for many sex workers and is doing very little to protect underage prostitutes who are being trafficked into the trade.

On the other hand, there is ample evidence that decriminalizing adult prostitution and allowing sex workers to advertise online reduces the level of violence not only against prostitutes but all women. In a recent study, researchers in the Netherlands found that when major cities in that country opened tippelzones, or areas where street prostitutes could work legally, reports of rape and sexual abuse declined by as much as 30 to 40 percent in the first two years after the zones were opened. And now we have evidence that providing American sex workers with a means to advertise their services online and screen clients may significantly reduce the likelihood of their being murdered.

What more do we need to know to change our foolhardy policies and start doing a better job of protecting all women, including those who choose to sell sex?

This blog has been cross-posted on The Huffington Post.