Viability of Web-Based Respondent-Driven Sampling of Belgian Men Who Have Sex With Men: Process Evaluation

Obtaining a representative sample is a substantial challenge when undertaking health research among hidden and hard-to-reach populations such as men who have sex with men Web-based respondent-driven sampling (WEB RDS) was developed to overcome such sampling challenges and to create population estimates based on network and sampling characteristics. Despite a decade of research, it remains unclear whether WEB RDS is suitable for sampling hidden populations such as men who have sex with men.

This study aims to evaluate how viable the WEB RDS methodology is for obtaining a nationwide sample of men who have sex with men, suitable for population inference of sexual health characteristics, in Belgium.

We adapted the Medical Resource Council process evaluation framework for interventions, to evaluate an empirical WEB RDS. Viewing "WEB RDS" as a complex intervention with respondent-driven recruitment as the aim, we evaluated indicators of context, implementation, mechanisms of impact, and performance. We analyzed the data using a mixed methods approach that integrated findings from quantitative analysis, such as RDS diagnostics, and qualitative thematic analysis.

Sampling did not reach a sufficient sample size (n=193) to compensate for an RDS design effect of 3 and the number of recruitment waves was low (waves=7). A visual examination of the convergence and bottleneck plots indicates that many more waves of recruitment would be needed for population estimates to become independent of the seeds. However, producing further waves was impeded by challenges inherent to the research context and process. Men who have sex with men and their community organization representatives indicated that, in Belgium, men who have sex with men are overresearched, with low motivation for the topic of sexual health and digital etiquette dictating not sharing survey links. A moderate reward of €10-€30 (US $11.2-$33.6) with a dual incentive structure was insufficient to overcome these barriers.

This study indicates that WEB RDS, even with a moderate incentive, is not a viable sampling strategy for obtaining valid population estimates of sexual health traits of men who have sex with men in Belgium. The study emphasizes the need to understand men who have sex with men research motivation and topic saliency. Additionally, the study highlights the importance of digital etiquette. Finally, the study showcases the use of the adapted Medical Research Council framework for evaluating WEB RDS methodology.