HIV infection risk and condom use among sex workers in Senegal: evidence from the list experiment method

Social desirability bias, which is the tendency to under-report socially undesirable health behaviours, significantly distorts information on sensitive behaviours that is gained from self-reports. As a result, self-reported condom use among high-risk populations is thought to be systematically over-reported, and it is impossible to identify the determinants of condom use. The main objective of the article is to elicit unbiased information on condom use among female sex workers (FSWs) using the double list experiment method to analyse the role of HIV infection and exposure to HIV prevention methods in condom use. More specifically, the difference in levels of condom use between HIV-positive and HIV-negative FSWs is estimated. In addition, the role of FSWs' registration and participation in a pre-exposure prophylaxis (PrEP) demonstration project in condom use is considered. A list experiment was designed to elicit condom use information from 786 FSWs in Senegal who were surveyed in 2015 and 2017. Using the list experiment method, participants were randomly assigned to one of two groups (treatment or control) and were asked to report the number of statements they agreed with. Respondents assigned to the control group were presented with three non-sensitive items, whereas those allocated to the treatment group were presented with the same three statements plus the sensitive item (e.g. ‘I used a condom during my last intercourse with a client'). Comparing the average number of sentences that were agreed with in both groups provides an estimation of the condom use rate in the treatment group and estimating such prevalence for several sub-groups allows the role of HIV infection risk in condom use to be identified. The percentage of FSWs using condoms in their last sexual intercourse with a client was 80% in 2015 and 78% in 2017, which was significantly lower than the 97% obtained in the face-to-face surveys in both waves. When estimating condom use among sub-groups with the list experiment method, we found that condom use among HIV-positive FSWs was only 34%, which was 47 percentage points lower than condom use among HIV-negative FSWs. We also found that registered FSWs are more likely to use condoms than clandestine FSWs. However, we did not find any difference in condom use between FSWs who were enrolled in the PrEP demonstration project and those who were not enrolled. Health policies should therefore aim to increase condom use among HIV-positive FSWs.