Measuring a hidden population: A novel technique to estimate the population size of women with sexual violence-related pregnancies in South Kivu Province, Democratic Republic of Congo

•Estimating the size of hidden populations often relies on difficult to obtain data.•Respondent-driven sampling (RDS) is often used to sample hidden populations.•RDS collects data on recruitment and social network size.•We introduce a method (SS-PSE) to estimate population sizes using RDS data.•SS-PSE reduces the cost and effort of estimating the size of hidden populations.

Successive sampling (SS)-population size estimation (PSE) is a technique used to estimate the sizes of hidden populations using data collected in respondent-driven sampling (RDS) surveys. We assess past estimations and use new data from an RDS survey to calculate a new PSE. In 2012, 852 adult women in South Kivu Province, Democratic Republic of Congo, who self-identified as survivors of sexual violence, resulting in a pregnancy, since the start of the war (in 1996) were sampled using RDS. We used imputed visibility, enrollment order, and prior estimates for PSE using SS-PSE in RDS Analyst. Prior estimates varied between Congolese local experts and researchers. We calculated the PSE of women with a sexual violence-related pregnancy in South Kivu using researchers' priors to be approximately 17,400. SS-PSE is an effective method for estimating the population sizes of hidden populations, useful for providing evidence for services and resource allocation. SS-PSE is beneficial because population sizes can be calculated after conducting the survey and do not rely on separate studies or additional data (as in network scale-up, multiplier, and capture-recapture methods).