Abstract
Background The self-reported European Health Literacy Survey Questionnaire (HLS-EU-Q47) is a widely used measure for population health literacy. Based on confirmatory factor analyses and Rasch modelling, the short form HLS-Q12 was developed to meet the Rasch unidimensional measurement model expectations. After its publication, there was a worldwide call to identify HLS-Q12 cutoff scores and establish clearly delineated standards regarding the skills assessed. This study therefore aims to identify the HLS-Q12 scores associated with statistically distinct levels of proficiency and to construct a proficiency scale that may indicate what individuals typically know and can do at increasingly sophisticated levels of health literacy. Methods We applied the unidimensional Rasch measurement model for polytomous items to responses from 900 randomly sampled individuals and 388 individuals with type 2 diabetes. Using Rasch based item calibration, we constructed a proficiency scale by locating the ordered item thresholds along the scale. By applying Wright’s method for the maximum number of strata, we determined the cutoff scores for significantly different levels. By directly referring to item content that people who achieved the cutoff scores viewed as ‘easy’, we suggested what these gradually more advanced levels of health literacy might mean in terms of item content. Results Analysing the population sample, we identified statistically distinct levels of health literacy at the empirically identified cutoff scores 27, 33 and 39. We confirmed them by analysing the responses from individuals with diabetes. Using item calibration, the resulting HLS-Q12 proficiency scale expresses typical knowledge and skills at these three statistically distinct levels. The scale’s cumulative nature indicates what it may mean qualitatively to move from low to high health literacy. Conclusions By identifying levels of health literacy, we may initiate the improvement of current models of health literacy. Determining how to adapt information to patients’ health literacy level is a possible clinical outcome. A substantial methodological outcome is the inevitability of Rasch modelling in measurement. We found that Wright’s method identified rating scale cutoff scores consistently across independent samples. To reveal sources of potential biases, threats to validity and imprecision of benchmarks, replication of our study in other contexts is required
Measuring ability to assess claims about treatment effects: a latent trait analysis of items from the ‘Claim Evaluation Tools’ database using Rasch modelling
