Alternate methods of framing information about medication side effects: incremental risk versus total risk of occurrence.

Communications of treatment risk, such as medication package inserts, commonly report total rates of adverse reactions (e.g., 4% get heartburn with placebo, 9% with medication). This approach, however, requires mental arithmetic to distinguish the incremental risk caused by medication (here, 5%) from the total post-treatment risk. In two Internet-administered survey experiments (N = 2,012 and 1,393), we tested whether explicitly reporting the incremental risk and framing it as the "additional risk" of complications influenced people's impressions of adverse event risks. Study 1 compared side-by-side displays of total risks against sequential presentations that highlighted the incremental risk, using both text and graphical formats. Results showed that incremental risk formats significantly lowered participants' worry about complications and reduced biases caused by varying the risk denominator. Study 2 unpacked this factor and showed that its effect on both perceived likelihood and worry derives primarily from the incremental risk framing rather than from sequential presentation. Explicitly reporting incremental risk statistics appears to facilitate recognition of how much risk already exists at baseline. Presenting adverse reaction risks in this manner may improve patient comprehension of the effects of treatment decisions and support effective risk communication.