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A Test of Numeric Formats for Communicating Risk Probabilities

Food Policy Institute, Rutgers, The State University of New Jersey, New Brunswick, cuite{at}aesop.rutgers.edu

Neil D. Weinstein, PhD

Department of Family and Community Medicine, University of Arizona College of Medicine, Phoenix

Karen Emmons, PhD

Harvard School of Public Health, Dana Farber Cancer Center, Boston, Massachusetts

Graham Colditz, MD, DrPH

Alvin J. Site-man Cancer Center, Washington University School of Medicine, St. Louis, MO

Background. Because people frequently encounter information about the probability of health risks, there is a need for research to help identify the best formats for presenting these probabilities. Methods. Three waves of participants were recruited from visitors to a cancer-related Internet site. Participants were presented with a hypothetical scenario that required them to perform 2 mathematical operations of the types that might be encountered in discussions of risk. Each wave encountered different operations. The operations used were compare, halve, triple, add, sequence, and tradeoff. Three numeric formats for communicating risk likelihoods were tested: percentages (e.g., 12%), frequencies (e.g., 12 in 100), and 1 in n (e.g., 1 in 8), and many levels of risk magnitude were crossed with the 3 formats. Results. The total sample of 16,133 individuals represented an overall participation rate of 36.1%. Although the relative performance of the formats varied by operation, aggregated across operations, the percentage and frequency formats had higher overall accuracy rates than the 1-in-n format (57% and 55% v. 45%, respectively). Participants with less education, African Americans, Hispanics, and women had more difficulty with the mathematical operations. Discussion. Percentage and frequency formats facilitate performance of simple operations on risk probabilities compared with the 1-in-n format, which should usually be avoided.

Key Words: risk • risk likelihood • probability • risk format • risk communication • patient-provider communication. (Med Decis Making 2008;28:377—384)

This version was published on June 1, 2008

Medical Decision Making, Vol. 28, No. 3, 377-384 (2008)
DOI: 10.1177/0272989X08315246


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