Effects of communicating social comparison information on risk perceptions for colorectal cancer.

People typically believe their health risks are lower than those of others (i.e., optimistic bias). We sought to increase perceptions of colorectal cancer (CRC) risk among adults aged 50-75 who were nonadherent to fecal occult screening (FOBT). 160 participants were randomized to receive information about the following: (1) general CRC risk factors (control), (2) general and tailored CRC risk factor feedback (absolute risk group), or (3) absolute CRC risk factor feedback plus CRC feedback as to how their total number of risk factors compared with that of others (absolute plus comparative risk group). Primary outcomes were perceived absolute and comparative risks, attitudinal ambivalence toward FOBT, and screening intentions; the secondary outcome was return of a completed FOBT. Participants who were told that they had more than the average number of risk factors believed their comparative CRC risk was higher than that of controls and of participants informed that they did not have more than the average number of risk factors. Perceived absolute risk did not vary by group. Participants who received social comparison risk factor feedback expressed greater intentions to screen via a FOBT than participants who received absolute risk feedback and controls; they also expressed less ambivalence about FOBT screening than controls. Although not statistically significant, participants informed they were at lower comparative risk had the highest proportion of completing an FOBT than any other group. These results suggest that providing social comparison CRC risk factor feedback can effectively reduce optimistic comparative risk perceptions. Contrary to findings of models of health behavior change, being informed that one does not have more than the average number of CRC risk factors, while resulting in lower evaluations of perceived comparative risk, did not result in higher ambivalence toward and lower intentions to screen using FOBT or the lowest rate of screening.