English-Spanish equivalence of the Health Literacy Assessment Using Talking Touchscreen Technology (Health LiTT).

Unbiased measurement instruments are needed to reliably estimate health literacy in diverse populations. The study aimed (a) to evaluate measurement equivalence of Health Literacy Assessment Using Talking Touchscreen Technology (Health LiTT) and (b) to compare Health LiTT scores between English- and Spanish-speaking individuals. Health LiTT and several patient-reported outcome instruments were completed by adult patients receiving care for type 2 diabetes at a safety net clinic. English-Spanish measurement equivalence was evaluated with an item response theory approach to differential item functioning (DIF) detection and impact. Health LiTT scores were compared by language using multivariable linear regression. Approximately equal numbers of English-speaking patients (n=146) and Spanish-speaking patients (n=149) with type 2 diabetes were enrolled. English participants were primarily non-Hispanic Black (65%); all Spanish participants were Hispanic. Six Health LiTT items were flagged for DIF. The Pearson correlation between unadjusted and DIF adjusted scores was 0.995; the mean difference of individual difference scores was 0.0005 (SD=0.0888). After adjusting for predisposing characteristics, enabling resources and need for care, Health LiTT scores were comparable for Spanish-speaking individuals versus English-speaking individuals. The effect of DIF items on Health LiTT scores appeared to be trivial. English-Spanish equivalence of Health LiTT will permit researchers to determine the independent effects of limited English proficiency and limited literacy.