Gay men's estimates of the likelihood of HIV transmission in sexual behaviours

In 3 studies we recorded gay men's estimates of the likelihood that HIV would be transmitted in various sexual behaviours. In Study 1 (data collected 1993, n=92), the men were found to believe that transmissibility is very much greater than it actually is; that insertive unprotected anal intercourse (UAI) by an HIV-infected partner is made safer by withdrawal before ejaculation, and very much safer by withdrawal before either ejaculation or pre-ejaculation; that UAI is very much safer when an infected partner is receptive rather than insertive; that insertive oral sex by an infected partner is much less risky than even the safest variant of UAI; that HIV is less transmissible very early after infection than later on; and that risk accumulates over repeated acts of UAI less than it actually does. In Study 2 (data collected 1997/8, n=200), it was found that younger and older uninfected men generally gave similar estimates of transmissibility, but that infected men gave somewhat lower estimates than uninfected men; and that estimates were unaffected by asking the men to imagine that they themselves, rather than a hypothetical other gay man, were engaging in the behaviours. Comparison of the 1993 and 1997/8 results suggested that there had been some effect of an educational campaign warning of the dangers of withdrawal; however, there had been no effect either of a campaign warning of the dangers of receptive UAI by an infected partner, or of publicity given to the greater transmissibility of HIV shortly after infection. In Study 3 (data collected 1999, n=59), men induced into a positive mood were found to give lower estimates of transmissibility than either men induced into a neutral mood or men induced into a negative mood. It is argued that the results reveal the important contribution made to gay men's transmissibility estimates by cognitive strategies (such as the 'availability heuristic' and 'anchoring and adjustment') known to be general characteristics of human information-processing. Implications of the findings for AIDS education are discussed. <br />