Validation of the Subjective Numeracy Scale: Effects of Low Numeracy on Comprehension of Risk Communications and Utility Elicitations

BACKGROUND: In a companion article, the authors describe the Subjective Numeracy Scale (SNS), a self-assessment of numerical aptitude and preferences for numbers that correlates strongly with objective numeracy. OBJECTIVE: The objective of this article is to validate the Subjective Numeracy Scale using measures of subjects' capacity to recall and comprehend complex risk statistics and to complete utility elicitations. RESEARCH DESIGN: The study is composed of 3 general public surveys: 2 administered via the Web and 1 by paper and pencil. Subjects. Studies 1 and 3 surveyed 862 and 1234 people, respectively, recruited via a nationwide commercial Internet survey panel. Study 2 involved 245 people who completed paper-and-pencil surveys in a Veterans Administration hospital. MEASURES: The authors tested whether one's score on the SNS predicted the likelihood of correct recall and interpretation of risk information (studies 1 and 2A) or the likelihood of effectively completing a time tradeoff or person-tradeoff utility elicitation (studies 2B and 3). In Studies 1 and 2, the authors also tested whether an objective test of quantitative ability would predict performance. RESULTS: In all studies, survey participants with higher SNS scores performed significantly better than other respondents. The predictive ability of the SNS approached that observed for objective numeracy. CONCLUSIONS: The SNS effectively predicts both risk comprehension and completion of utility elicitations without requiring survey participants to complete time-consuming and stress-inducing mathematics tests. The authors encourage the use of the SNS in a variety of health services research contexts.