Introduction

In general, little attention is given to homosexual role behaviour as a factor in the sexual transmission of HIV. Models that include variations in sexual behaviour are usually restricted to heterogeneity in sexual partner-change and the manner in which subpopulations mix. Following Trichopoulos et al (1988), Wiley and Herschkorn (1989), van Griensven et al. (1990), we lay emphasis on homosexual role behaviour (role separation) as a factor influencing the spread of HIV in homosexual populations. If there are large differences between the risks of receptive and insertive anal intercourse, with the latter carrying only minimal risk, then one may expect that changes in role behaviour distributions influence the spread of HIV. As pointed out by Trichopoulos et al. (1988), role separation is expected to reduce the spread of HIV since those who are practicing insertive intercourse would be at low risk and those practicing receptive intercourse would not be at very high risk because of the low prevalence of HIV among their sexual partners.

Based on this conjecture Wiley and Herschkorn (1989) constructed a theoretical model for exploring the effect of differentiation of roles in anal intercourse on the size of AIDS epidemics in homosexual populations. Under the assumption of no risk associated with insertive anal intercourse it was shown that epidemic intensity increases with increasing size of the dual-role (both insertive and receptive) subpopulation. Their paper, however, was not concerned with the analysis of specific data. Recently van Griensven et al. (1990) and van Zessen and van Griensven (1992) provided empirical evidence, using data from the first two cycles of the Amsterdam cohort, that homosexual role behaviour is a factor in the spread of HIV.