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Research has demonstrated that individual differences in numeracy may have important consequences for decision making. In the present paper, we develop a shorter, psychometrically improved measure of numeracy—the ability to understand, manipulate, and use numerical information, including probabilities. Across two large independent samples that varied widely in age and educational level, participants completed 18 items from existing numeracy measures. In Study 1, we conducted a Rasch analysis on the item pool and created an eight‐item numeracy scale that assesses a broader range of difficulty than previous scales. In Study 2, we replicated this eight‐item scale in a separate Rasch analysis using data from an independent sample. We also found that the new Rasch‐based numeracy scale, compared with previous measures, could predict decision‐making preferences obtained in past studies …