Individual and aggregate level change in sexual behavior among gay men at risk for AIDS.

Until an effective vaccine or treatment for AIDS is developed, the rate of spread of the epidemic will be determined primarily by the willingness of infected and at-risk individuals to refrain from behaviors implicated in the spread of the disease. Consequently, public health efforts have focused on educating these populations about the dangers inherent in certain practices. To date, the impact of these educational activities has been most extensively studied with regard to gay and bisexual men. Researchers, however, seem not always to appreciate the necessity to examine change at two levels of analysis--the individual and the aggregate because it is possible to draw different but valid conclusions about the nature of change, depending upon the level of analysis used. A series of models for examining individual and aggregate level change are described. These models are then used to examine whether there is evidence of change over a 6-month period in the sexual behavior of a sample of gay men from New York City. The data reveal evidence of a significant trend in the direction of safer sexual behavior at both the individual and aggregate level.