The report goes into a fairly detailed explanation of how they made the link between the number of phone numbers and how many providers this represented. Personally, I thought their whole argumentation unconvincing and the methodology to be flawed. It is based on the approach taken by a single prior study done in 2008, that the panel itself thought was questionable.
Basically they have no idea how many there are before and after. No one, in any country has any idea exactly how many escorts there are at any given time. Especially since many of them are working on and off.
Do they make any distinction between agencies and independent providers for the phone numbers? Do they consider that many indys simply use e-mail instead of phone number?
After a change from legal to criminal, you can expect advertisement to change. We could expect prostitution to be 10-20% less visible than before. That is no measure of how many providers there actually is. In fact even a real 10% decrease in providers does not mean there is a decrease in the demand. It's hard to know what the demand is, because it's very easy for these men to go to Holland or Germany or Denmark or even Finland to get it.
It reminds me of that study in the US where they estimate the number of trafficked underage by asking people to guess the age from the pictures in the ads.





