'I'll do what they did": social norm information and cancer treatment decisions

Using a cancer-treatment scenario, we tested whether descriptive norm information (e.g., the proportion of other people choosing a particular treatment) would influence people's hypothetical treatment choices.

Women from an Internet sample (Study 1 N=2238; Study 2 N=2154) were asked to imagine deciding whether to take adjuvant chemotherapy following breast cancer surgery. Across participants, we varied the stated proportion of women who chose chemotherapy. This descriptive norm information was presented numerically in Study 1 and non-numerically in Study 2.

The descriptive norm information influenced women's decisions, with higher interest in chemotherapy when social norm information suggested that such chemotherapy was popular. Exact statistics about other people's decisions had a greater effect than when norms were described using less precise verbal terms (e.g., "most women").

Providing patients with information about what other people have done can significantly influence treatment choices, but the power of such descriptive norms depends on their precision.

Communication of descriptive norms is only helpful if prevailing decisions in the population represent good clinical practice. Strategic presentation of such statistics, when available, may encourage patient outliers to modify their medical decisions in ways that result in improved outcomes.