The Effects of Absolute Risks, Relative Risks, Frequencies, and Probabilities on Decision Quality

It is important to understand how the quality of people's decision making may be affected by the format used to present treatment benefits. Two experiments compared the accuracy of presenting the benefits of cancer screening tests or vaccines using either absolute or relative risk formats that included baseline risk information. Moreover, the absolute and/or baseline risks were presented using either natural frequencies or probabilities. In both experiments, accuracy was measured by the sensitivity of choices to differences in absolute rather than relative risks. Experiment 1 showed no significant differences in sensitivity between the relative and absolute risk formats when the risks were presented as natural frequencies. Sensitivity was, however, poor in both probability versions. Experiment 2 tested the natural frequency versions more stringently by presenting choices with different levels of difficulty. The author found that decision quality was significantly less affected by increases in difficulty in the absolute risk format. Presenting baseline risks using natural frequencies may help to reduce the biasing effects of relative risks but decision quality may not be on a par with the accuracy of decisions made when absolute risks are presented in natural frequency formats.