Respondent-driven sampling to assess cumulative lifetime incidence of abortion in Soweto, South Africa: A methodological assessment

Respondent-driven sampling (RDS) is a potential strategy for addressing challenges in accurate abortion incidence estimation, but relies on often untested assumptions. We conducted an RDS study to estimate the cumulative lifetime abortion incidence in Soweto, South Africa, evaluate whether RDS assumptions were met, and compare RDS estimates of incidence to estimates adjusted for employment and age based on census data.

A total of 849 participants were recruited from 11 seeds between April and December 2018. The assumptions that individuals can identify target population members and approximation of sampling with replacement was met. There were minor violations of the assumptions of seed independence from the final sample, and reciprocity of ties. Assumptions of accurate degree reporting and random recruitment were not met. Failure to meet assumptions yielded a sample with different employment characteristics than the target population, which was not resolved by standard RDS methods.

The RDS estimate of cumulative lifetime abortion incidence was 12.1% (95% CI: 9.8%, 14.3%), and the employment-adjusted estimate was 16.9% (95% CI: 12.8%, 22.1%). We caution researchers in using RDS for representative estimates of abortion incidence. Post-survey weights to adjust for differences in characteristics between the sample and target population may yield more representative results.