Validation of the Assessments of Adult Health Literacy: A Rasch Measurement Model Approach.

Background: Both the World Health Organization and U.S. Department for Health and Human Services have emphasized the importance of health literacy (HL) to improving population health and reducing health disparities. HL includes three core areas/qualities: functional (i.e., health-related reading, writing, and numeracy), interactive/communicative (i.e., skills for interacting with multiple constituents and sources of information and navigating the health environment), and critical (i.e., personal and community advocacy for health). HL is implicated in medical adherence, preventive health, mental health stigma and help-seeking, and health decision-making. Though HL is critical to health and health decision-making, research on HL is still relatively limited, with most research focusing on functional HL. A major gap in research is related to the lack of measurement of interactive and critical HL. To address this gap, this study modified and assessed the validity of the Assessments of Adolescent Health Literacy (AAHL-Adolescent), test-based assessments of adolescents' functional, interactive, and critical HL, in an adult sample. Methods: One item from the AAHL-Adolescent item bank was modified to be more appropriate for an adult sample. Adults (n=2346) completed a measurement battery that included the HL item bank (12 functional, 15 interactive, and 9 critical HL questions), Newest Vital Sign (NVS), Single-Item Literacy Scale (SILS), demographics, and questions about HL-related behaviors. The assessments were evaluated and validated using Rasch measurement models. Convergent and criterion validity were assessed. Results: The final 7-item functional, 10-item interactive, and 7-item critical HL assessments and their composite (24 items) fit their respective Rasch models. Item-level invariance was established for gender, ethnicity, education, and age across all assessments. Differential item functioning for race was noted for two items on the interactive HL assessments. Good convergent validity with the NVS and SILS and good criterion validity with the HL-related behaviors were observed for all assessments. Conclusions: The AAHL-Adult is the first test-based instrument validated in the U.S. that includes assessments for all three core qualities of HL. These assessments have utility across multiple settings, including public health program planning and evaluation, intervention development and evaluation, and clinical settings.