This document is a research brief based on a contribution by Jan J. M. van Dijk, Maarten Cruyff, Peter G. M. van der Heijden and Suzanne L. J. Kragten-Heerdink. It presents Multiple Systems Estimation for estimating the number of victims of trafficking in persons by generating a sound estimate of the ‘dark figure’, which is the unknown data that is undetected and unreported. 

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