Testing implicit assumptions and explicit recommendations: the effects of probability information on risk perception

When people underestimate a risk, often probability information is communicated because of the implicit assumption that it will raise people's risk estimates as a result of these objective facts. Also, scientific literature suggested that stressing the cumulative aspects of a risk might lead to higher susceptibility perceptions than only emphasizing the single incident probability. Empirical evidence that supports the effectiveness of these strategies, however, is lacking. In two studies, we examined whether cumulative and single incident probability information on sexually transmitted infections leads to higher perceived susceptibility for Chlamydia and HIV. Contrary to assumptions and recommendations, results showed that both types of probability information may result in people feeling less susceptible toward Chlamydia and having less intention to reduce the risk. For HIV, no effects were found. These results contradict implicit assumptions and explicit recommendations concerning the effects of probability information on risk perceptions.