Percentages are a better format for conveying medical risk than frequencies

For patients to make informed decisions about their health care, it is essential that they understand the risks associated with various treatments. However, risks can be framed in different ways, and past research has yielded conflicting results about which format is easiest for people to comprehend. Frequencies (e.g., 1 out of 4) and percentages (e.g., 25%) are common ways to communicate risk, and the goal of this study was to explore how these formats affected the comprehension of different numerical values. A sample of American adults (N = 141) was recruited via Amazon’s Mechanical Turk to take a survey on Qualtrics. Participants indicated their preference for frequencies or percentages and then answered a set of questions to evaluate their skill at working with the two formats when the values were small, large, complex, or simple. Participants reported equivalent comfort levels with risks framed as percentages and frequencies, but interestingly, they performed significantly better on questions asked using percentages than frequencies. These findings indicate that percentages should be used instead of frequencies when presenting risk information to patients, regardless of the size and complexity of the numerical value represented.