My view is that in either prostitution or trafficking we need more research and we need more data collection. The data collection requires a coherent system of data collection. It's not like a country where every municipality is entitled or not to have data collection so you cannot compare and it's not reliable. So I believe it's important that this research is done and also that the official bodies have the same standards of data collection regarding these types of figures.
But let me tell you, and I think it's important and I profit from your question, that some very important academic research was done recently by the London School of Economics and Political Science, the University of Heidelberg, and the German Institute for Economic Research of Berlin. They studied the available data in 150 countries regarding prostitution and the trafficking of human beings. They came to the conclusion that you have the scale effect. This means that if you legalize prostitution then you have an expansion of the sexual business and then you need more people to be trafficked to supply that scale effect.
But the substitution effect is also true. If you legalize prostitution then you don't need any more of the illegal and trafficked ones. So this would be apparently in contradiction. They came to the conclusion that the scale effect prevails. This means that if you legalize prostitution you will have more trafficked people to supply that industry.