Prevalence does not seem to be currently used to measure the impact of anti-forced labour, anti-sex trafficking or other anti-slavery projects, although there is no evidence to suggest that it is not a suitable indicator. Instead, the following types of indicators have been used or suggested by experts for measuring the impact of justice interventions: changes in knowledge or behaviour; focus on institutional changes within the criminal justice (CJ) system; measuring complaints, investigations, arrests, convictions and timeliness; and victim experience with the CJ system. Using a group or ‘basket’ of indicators relating to the same policy objective provides a more reliable assessment.
Limited information is available on methodologies that have been used for estimating/measuring the extent of trafficking or forced labour in a particular area. One recurring theme is the need for “place-randomized trials”, whereby data obtained from interventions in ‘hot spots’ is compared with locations where there have been no interventions, to assess whether increased criminal justice in one area displaces the problem to another area.
Prevalence is generally agreed to be difficult to record through surveys, but reliance on official data is also thought to be problematic for reporting hidden crimes. Furthermore, connecting a programme evaluation to crime rates requires knowledge of the range of influences on crime rates, the relative magnitudes of those influences, and how they may interact with one another and with the operation and outcomes of the relevant anticrime programme.
