THE ECONOMIST analysed 190,000 profiles of female sex workers on websites where customers post reviews. The data cover 84 cities in 12 countries, with the biggest number of workers in America and most of the rest in big cities in rich countries. According to the analysis, the price of an hour of sex with a female prostitute has been dropping fairly steadily in recent years. In 2006 the average cost was around $340. By 2014 it had dropped to about $260.

A prostitute’s hourly rate depends on a variety of factors, including the services she provides and her reported physical characteristics. Those who conform most closely to the stereotypical version of Western beauty—slim, with long blonde hair and full breasts—earn the most. Those who provide niche services—for example, sex workers who will accept two male clients at once—also command a premium. Location matters too. Prostitutes in San Francisco, where the cost of living is high, charge more than those in cheaper cities such as Prague.

The fall in prices can be attributed in part to the 2007–08 financial crisis. Even places that have escaped its worst effects, such as London, have been hit. In cities such as Cleveland, Ohio, where unemployment peaked at 12.5% in 2010, prices have plummeted. Migration is also driving down prices. Big, rich cities, such as London, attract a steady inward flow of poorer migrants, who are prepared to do all kinds of work for lower wages than locals. In places such as Norway, where local prostitutes had tried to standardise prices, growing numbers of migrant sex workers have made such unofficial price controls harder to sustain. The increase in people selling sex online—where it is easier to be anonymous—has probably boosted local supply. Meanwhile broader social changes may have reduced demand. Casual and adulterous sex is easier to find than in the past. Pre-marital sex is more acceptable and divorce easier, with the result that fewer frustrated single and married men turn to prostitutes. That drives prices down, too.

Sex workers complain that they are earning less than in the past. But their incomes may not have fallen as steeply as the decline in prices would suggest. The shift towards advertising and co-ordinating the sale of sex online means that prostitutes now rely less on intermediaries, such as brothels and agencies, pimps and madams. As a result, they may be able to keep a greater proportion of their income. But selling sex online brings new demands. Clients contact sex workers via their websites, by e-mail, through Facebook and Twitter. Some websites allow prostitutes to tell clients whether they are currently available; but that means going online frequently to update their status. Such work is time-consuming, so some prostitutes may end up paying someone to do it for them. For sex workers, as much as anyone, time really is money.

Dig deeper:

Why governments should stop trying to ban prostitution (August 2014)

How the internet is shaking up the oldest business (August 2014)

A sex worker explains why criminalisation is bad for her industry (August 2014)

Update: This blog post has been amended to remove the news peg.