Estimating the Prevalence of Forced Labor in the Fishing Industry in Puntarenas, Costa Rica: A Direct Comparison of Conventional Sampling and Vincent Link-Tracing Sampling Strategies

Author: Dank, Meredith; Zhang, Sheldon; Vincent, Kyle; Stoeltje, Mackenzie & Wang, Mengfei

Abstract: As part of the Prevalence Reduction Innovation Forum (PRIF), a prevalence study was conducted on forced labor in Costa Rica’s fishing industry. Two strategies were used for the target population of fishers: (1) A multistage probability proportional to size (PPS) household survey with a sample size of 1,017, and (2) Vincent link-tracing sampling (VLTS) with a sample size of 1,009. The approaches produced similar findings on the prevalence of forced labor abuses. Both methodologies also found forced labor, as defined by the PRIF indicators, to affect roughly one of every five fishermen. We found that a multistage sampling design is not best suited, at least in the Costa Rican fishing industry context, for estimating the size of the fisher population; the estimate produced an extreme value suspected to be much higher than the local partners and research team expected. VLTS produced population size estimates closer to expectations. Field staff reported that VLTS was challenging to implement due to linking respondents from different waves. Findings also suggest the two strategies tapped into separate parts of the “hidden” population and also gave discrepant estimates on parts of the composition of the population. We advocate the exploration of hybrid methodologies whenever feasible in the future research.

Keywords: Costa Rica, human trafficking, link-tracing samplingm prevalence estimation, probability proportional to size