When does event valence affect unrealistic optimism?

"Unrealistic optimism" (UO) has been found to be greater for negative (i.e. undesirable) than for positive (i.e. desirable) events. In two studies, we tested whether this "valence effect" is explicable in terms of motivational processes. In each case, participants were students (n = 159 in Study 1, n = 90 in Study 2), UO for the same health event was measured, and valence was manipulated by framing the event either negatively or positively. The degree to which the event would be expected to evoke concern was varied by manipulating the ease with which it could be avoided (Study 1) or the severity of its consequences (Study 2). A similar pattern of results was found in each study: the valence effect was exhibited in the condition where the event would have evoked concern, but not in the condition where it would have evoked little concern. The findings are in accord with an explanation of the valence effect in motivational terms. Implications for health education are discussed.