Background Health numeracy can be defined as the ability to understand and use numeric information and quantitative concepts in the context of health. We previously reported the development of the Numeracy Understanding in Medicine Instrument (NUMi); a 20-item test developed using item response theory. We now report the development and validation of a short form of the NUMi. Methods 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. Results The 8-item scale had adequate reliability (Cronbach's alpha: 0.72) and was strongly correlated to the 20-item NUMi (0.92). The S-NUMi scores were strongly correlated with the Lipkus numeracy test (0.62), Wide Range of Achievement Test-Mathematics (WRAT-M) (0.72), and Wonderlic cognitive reasoning test (0.76). Moderate correlation was found with education level (0.58) and print literacy as measured by the TOFHLA (0.49). Conclusion The short Numeracy Understanding in Medicine Instrument is a reliable and valid measure of health numeracy feasible for use in clinical and research settings.

BACKGROUND:The Spanish-speaking population in the U.S. is large and growing and is known to have lower health literacy than the English-speaking population. Less is known about the health numeracy of this population due to a lack of health numeracy measures in Spanish. OBJECTIVE: we aimed to develop and validate a short and easy to use measure of health numeracy for Spanish-speaking adults: the Spanish Numeracy Understanding in Medicine Instrument (Spanish-NUMi). DESIGN: Items were generated based on qualitative studies in English-and Spanish-speaking adults and translated into Spanish using a group translation and consensus process. Candidate items for the Spanish NUMi were selected from an eight-item validated English Short NUMi. Differential Item Functioning (DIF) was conducted to evaluate equivalence between English and Spanish items. Cronbach's alpha was computed as a measure of reliability and a Pearson's correlation was used to evaluate the association between test scores and the Spanish Test of Functional Health Literacy (S-TOFHLA) and education level. PARTICIPANTS: Two-hundred and thirty-two Spanishspeaking Chicago residents were included in the study. KEY RESULTS: The study population was diverse in age, gender, and level of education and 70 % reported Mexico as their country of origin. Two items of the English eightitem Short NUMi demonstrated DIF and were dropped. The resulting six-item test had a Cronbach's alpha of 0.72, a range of difficulty using classical test statistics (percent correct: 0.48 to 0.86), and adequate discrimination (item-total score correlation: 0.34-0.49). Scores were positively correlated with print literacy as measured by the S-TOFHLA (r = 0.67; p < 0.001) and varied as predicted across grade level; mean scores for up to eighth grade, ninth through twelfth grade, and some college experience or more, respectively, were 2.48 (SD ± 1.64), 4.15 (SD ± 1.45), and 4.82 (SD ± 0.37). CONCLUSIONS: The Spanish NUMi is a reliable and valid measure of important numerical concepts used in communicating health information.KEY WORDS: cross cultural research; health numeracy; health literacy; measurement; Spanish language.

A practice analysis, in which an appropriate sample of professionals is asked to describe what they do in their practices, is considered an essential part of the content-related validity evidence for licensure and certification tests. This article examines the precision of estimates of the mean frequencies for categories of activities in an activity inventory administered on two occasions about 6 weeks apart. In particular, it explores the variability in estimates of the mean frequencies for categories due to the sampling of respondents, activity statements, and occasions. The results suggest that samples of 200 respondents, about 10 to 20 activity statements per category, and one occasion are adequate for estimating the mean frequency for each category.

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