Assessment of non-response bias in a probability household survey of male same-gender sexual behavior.

OBJECTIVE: To assess non-participation bias in a survey of male sexual behavior. MATERIAL AND METHODS: A household survey was carried out in 1992-1993 using a probability sampling frame in Mexico City. Demographic variables were available for all eligible men. The extent of non-participation bias was estimated using a version of the Heckman method, which utilizes two equations, one to predict participation and the other to predict reports of same-gender sexual behavior. RESULTS: A total of 8,068 of the 13,713 eligible men completed a face-to-face questionnaire (response rate 59%); 173 men (2.1%) reported bisexual behavior in their lifetime, and 37 (0.4%) reported only male partners. Survey participation was predicted using demographic variables: 67% of the observations were correctly predicted by a probit regression model: 82% of participants and 53% of non-participants (pseudo-r2 = 0.13). Same-gender sexual behavior was predicted by variables indicating attachment to gay/bisexual social networks, history of sexually transmitted diseases, positive attitudes towards gay and bisexual males, and lack of support from male relatives. Ninety-seven per cent of the cases was correctly predicted by the probit model (pseudo-r2 = 0.14). The correlation between these two equations was not statistically significant. CONCLUSIONS: These results indicate that prevalence estimates of same-gender sexual behavior among Mexico City men were not biased by selective survey participation. Careful selection and training of household interviewers may have assisted in minimizing potential bias.

A model for the AIDS epidemic in Mexico: short-term projections.

As in many developing countries, the AIDS epidemic in Mexico has become a major public health problem. Given the competition for scarce health resources in Mexico, where hospitals are overcrowded and care for AIDS patients is often unavailable, planning depends on accurate estimates of the incidence of AIDS and the prevalence of HIV-1 infection. This article presents estimates of AIDS incidence in Mexico corrected for delays in reporting and short-term projections based on the corrected AIDS incidence. Trends in incidence cannot be assessed without such correction because only about 50% of AIDS cases are reported within 4 months of diagnosis. In addition to information on AIDS incidence, short-term projections also require estimates of the latency distribution between infection with HIV-1 and onset of AIDS. Latency periods with medians of 8 and 10 years lead to estimates that 22,000 and 24,000 new AIDS cases infected before June 1989 will be diagnosed between 1989 and 1994.