http://prostitution.procon.org/view.answers.php?questionID=000243
Nicklas Jakobsson, PhD, Research Fellow at Norwegian Social Research (NOVA), and Andreas Kotsadam, PhD, Postdoctoral Fellow at the University of Oslo, Norway, stated in their Feb. 2013 study titled "The Law and Economics of International Sex Slavery: Prostitution Laws and Trafficking for Sexual Exploitation, published in the European Journal of Law and Economics:
"Using two recent sources of European cross country data we show that trafficking of persons for commercial sexual exploitation... is least prevalent in countries where prostitution is illegal, most prevalent in countries where prostitution is legalized, and in between in those countries where prostitution is legal but procuring illegal."
....and....
Seo-Young Cho, Assistant Professor of Empirical Institutional Economics at Philipps-University of Marburg (Germany), Axel Dreher, Professor of International and Development Politics at Heidelberg University, Germany, and Eric Neumayer, Professor of Environment and Development at the London School of Economics and Political Science, UK, wrote in their Mar. 2013 paper for World Development titled "Does Legalized Prostitution Increase Human Trafficking":
"The scale effect of legalized prostitution leads to an expansion of the prostitution market, increasing human trafficking, while the substitution effect reduces demand for trafficked women as legal prostitutes are favored over trafficked ones. Our empirical analysis for a cross-section of up to 150 countries shows that the scale effect dominates the substitution effect. On average, countries where prostitution is legal experience larger reported human trafficking inflows..."