There are two competing hypotheses about the relationship between optimism versus pessimism and health behavior. On one hand, unrealistic optimism about invulnerability to health risks is hypothesized to cause decreased motivation for risk reduction and increased high-risk behavior. On the other hand, unrealistic optimism may provide individuals with specific health benefits, increase feelings of control over health status, and encourage positive health behaviors. This thesis examined the relationship between expectations about the likelihood of HIV infection and risk behavior among three cohorts of HIV-negative gay men. Study 1 examined a group of men who participated in a prospective natural history study of HIV infection, Study 2 investigated a cohort of patients presenting to clinic for non-occupational post-exposure prophylaxis (nPEP), and Study 3 examined a cohort of individuals receiving anonymous HIV antibody testing. Findings suggest different patterns of relationship between expectations and behavior for low- versus high-risk participants. For low-risk participants, pessimism was associated with higher levels of stress and negative affect (Studies 1 and 3), lower self-efficacy (Study 1), and more frequent thoughts about HIV, especially during sex (Studies 2 and 3). Among low-risk individuals, both extreme optimism and extreme pessimism appeared to motivate risk reduction, while more moderate expectancies were associated with lapsing into high-risk behavior (Study 1). For high-risk participants, both extreme optimism and extreme pessimism were associated with risk-taking, including increased substance use (Studies 1 and 2), especially before sex, and failure to complete the nPEP regimen (Study 2). In Study 3, unrealistic pessimism about HIV-status was associated with more high-risk behavior during the two-week waiting period for test results, and this relationship was especially strong for participants who had been low-risk prior to testing. It is possible that either extreme optimism or extreme pessimism about future infection may provide motivation to maintain risk reduction among low-risk individuals, but may provide rationalization to continue unsafe practices among high-risk individuals. Extreme pessimism appears to have an added cost while anticipating HIV test results. These findings have important implications for promoting risk-reduction within clinical settings.
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