Context: Although the ability to work with numbers is important to the practice of medicine, little is known about physician numeracy (basic skill with numbers).
Objective: To test medical students' numeracy and how it relates to the ability to interpret risk-reduction information.
Design: Randomized, cross-sectional survey.
Sample: 62 first-year medical students at the University of North Carolina at Chapel Hill medical school who attended a risk-communication seminar and had usable survey data (46% of the 134 students who received the survey).
Intervention: Students were given information about the baseline risk for developing a hypothetical disease and were randomly assigned to one of four risk-reduction presentations-relative risk reduction, absolute risk reduction, number needed to treat (NNT), or a combination of these three formats-about how two drugs would reduce this risk.
Outcome measures: Number of correct answers to three numeracy questions (stating that 500 heads would be expected in 1000 coin flips; converting "1% of 1000" to 10; and converting "1 in 1,000" to 0.1%). Correct data interpretation was judged with two tasks: a comparative task (i.e., state which drug provides greater benefit) and a quantitative task (i.e., calculate how much one of the drugs reduces disease risk).
Results: 77% of students answered all three numeracy questions correctly; 18% answered two correctly; and 5% answered one or none correctly. While 90% correctly stated which drug worked better, only 61% accurately interpreted the quantitative data. The ability to interpret data varied with numeracy: 71% of students who answered all three numeracy questions correctly also accurately interpreted the quantitative data, compared with 36% who answered two questions correctly and 0% who answered one or no questions correctly (P < 0.01). Correct quantitative interpretation was lower with the NNT format than with the other three formats (25% vs. 75%; P = 0.01).
Conclusions: Almost one quarter of first-year medical students in our study had trouble performing basic numerical tasks. Those who had trouble also seemed to have difficulty interpreting medical data. This difficulty seemed to be exacerbated by presenting data in the NNT format.