Health literacy measurement: a comparison of four widely used health literacy instruments (TOFHLA, NVS, HLS-EU and HLQ) and implications for practice

Background: Health literacy has evolved from a focus on individual skills to an interactive process influenced by relationships and the health system. Various instruments measure health literacy, developed from different conceptions and often for different measurement purposes. The aim of this study was to compare the properties of four widely used health literacy instruments: Test of Functional Health Literacy in Adults (TOFHLA), Newest Vital Sign (NVS), European Health Literacy Survey (HLS-EU-Q47), and Health Literacy Questionnaire (HLQ). Methods: This was a within-subject study comparing instrument performance. Composite reliability and Cronbach's alpha was used to measure internal consistency, floor/ceiling effects determined discriminate ability across low-to-high score ranges, and Spearman's R correlation coefficient was used to assess the relationship between instruments, particularly scales aiming to measure similar constructs. Results: Fifty-nine patients consented, with 43 completing all four instruments. Internal consistency was high for all scales (composite reliability range 0.76-0.95). Floor and ceiling effects were observed, with TOFHLA demonstrating the largest ceiling effect (>62) and NVS the only floor effect (18%). Only moderate correlations were found between TOFHLA and NVS (r =0.60) and between HLS-EU-Q47 and HLQ scales (r ~0.6). Conclusion: Our study found low to moderate correlations between the instruments, indicating they measure different constructs of health literacy. Clinicians and researchers should consider the intended measurement purpose and constructs when choosing an instrument. If the purpose of measurement is to understand reading, comprehension, and numeracy skills in individuals and populations, then performance based functional health literacy instruments such as the TOFHLA and NVS will be suitable. However, if the purpose is to generate insights into broader elements of health literacy, including social supports and relationships with health providers, then the HLS-EU and HLQ may be useful. The findings highlight the need for careful instrument selection to ensure meaningful and appropriate data interpretation. As improving population health literacy is a national priority in many countries, it is important that clinicians and researchers understand the measurement differences offered by different instruments to assist them to choose the right instrument for their measurement purpose.