Development and validation of the numeracy understanding in Medicine Instrument short form

Health numeracy can be defined as the ability to understand and use numeric information and quantitative concepts in the context of health. The authors previously reported the development of the Numeracy Understanding in Medicine Instrument (NUMi), a 20-item test developed using item response theory. The authors now report the development and validation of a short form of the NUMi. Item statistics were used to identify a subset of 8 items representing a range of difficulty and content areas. Internal reliability was evaluated with Cronbach's alpha. Divergent and convergent validity was assessed by comparing scores of the S-NUMI with existing measures of education, print and numeric health literacy, mathematic achievement, cognitive reasoning, and the original NUMi. The 8-item scale had adequate reliability (α=.72) and was strongly correlated to the 20-item NUMi (α=.92). S-NUMi scores were strongly correlated with the Lipkus Expanded Health Numeracy Scale (α=.62), the Wide Range of Achievement Test-Mathematics (α=.72), and the Wonderlic Cognitive Ability Test (α=.76). Moderate correlation was found with education level (α=.58) and print literacy as measured by the Test of Functional Health Literacy in Adults (α=.49). Results show that the short form of the NUMi is a reliable and valid measure of health numeracy feasible for use in clinical and research settings.