Risk Perception: Using Conditional Versus General Base Rates for Risk Communication1


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    Portions of this manuscript were presented at the Midwestern Psychological Association in May 2000. The authors thank Cory Grose, David Lishner, Brenda Treadwell, Debbi Sharp, and Eric Watland for their technical assistance.

Correspondence concerning this article should be addressed to Leilani Greening, Department of Psychiatry and Human Behavior, University of Mississippi Medical Center, Jackson, MS 39216. E-mail: LGreening@psychiatry.umsmed.edu


In general, people judge their chance of experiencing a health risk as being less than the general base rate because of their favorable status on risk factors (e.g., history of stroke). Presenting base rates for high and low risk groups (conditional base rates) were hypothesized to lessen people's tendency to adjust downward from the base rate because risk factors are included in conditional base rates (CBRs). Young (M= 19 years) and older women (M= 46 years) were presented with either a general base rate (GBR) or CBRs for high- and low-risk groups for 5 health risks. The CBR groups were significantly less likely to adjust their probability judgments from the base rate for the risk group that they believed applied to them (e.g., smoker vs. nonsmoker). The CBR effect was replicated in a second experiment in which women (M = 19 years) were informed of either a GBR, a CBR for a high-risk group, or a CBR for a low-risk group. The findings suggest that people might estimate subjective probabilities by considering both the base rate for a health risk and self-assessments on risk factors. Biases about one's status on risk factors, however, may limit people's identification with relevant risk groups and warrant further investigation.