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 Spanish-speaking 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 eight-item 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.
Keywords: Spanish language; cross cultural research; health literacy; health numeracy; measurement.