Despite ample evidence that numeracy is an important influence on patient understanding and use of health‐related information, there is a dearth of studies examining the concept's relationship to other individual differences measures that may underlie complex judgments in the health domain. In this study, we compared the relative contributions of selected extant numeracy measures and general intelligence and other measures to varied judgment and decision‐making outcomes. Two hundred participants completed numeracy items, subscales of the Wechsler Adult Intelligence Scales, the need for cognition scale, and four relevant outcome measures including risk estimation and medical data interpretation. A numeracy scale constructed using item response and confirmatory factor analyses was consistently the strongest predictor across all outcome measures and accounted for unique variance over and above general intelligence. The results support the concept of numeracy as an independent construct that merits consideration in patient communication. Copyright © 2013 John Wiley & Sons, Ltd.