ASSESSING PARTICIPATION BIAS IN A SEXUAL-BEHAVIOR SURVEY - IMPLICATIONS FOR MEASURING HIV RISK

Objectives: To assess the likelihood of participation bias in a large population-based sex survey, and its possible effect on estimates of H IV risk behaviours. Design: Construction of general hypotheses about n on-participants through comparisons of willing and unwilling participa nts. Methods: British adults aged 16-59 years were surveyed in 1990-19 91. Interviews consisted of a face-to-face section combined with a sel f-completion booklet (n = 18 876). Interviewers recorded interviewee e mbarrassment. Homosexual experience and number of lifetime heterosexua l partners (grouped 0, 1, 2 or more) were recorded prior to booklet of fer. Logistic regression was performed, with embarrassment and booklet refusal as outcome variables, assessing their association with sexual behaviour after controlling for demographic variables. Assuming that, in sexual behaviour, non-participants are closer to the embarrassed a nd the booklet refusers ('unwilling' participants) than to others, the se analyses provide an indication of the nature of participation bias. Results: Higher refusal and embarrassment rates were associated with both reporting no homosexual experience and fewer heterosexual partner s. Conclusions: Under our untestable assumption, these results are con sistent with non-participants being generally at lower risk of HIV inf ection. Methods need to be developed both to reduce participation bias in sex surveys, and to incorporate it in analysis.