Testing of the Thai Health Literacy Assessment Using Word List with Extended Questions to Test Comprehension (THLA-W+) in General Public

Abstract

Objective: To test the validity and reliability of the Thai Health Literacy Assessment Using Word List with Extended Questions to Test Comprehension (THLA-W+) in general public and to determine the cut-off score of the scale to interpret the level of health literacy (HL). Methods: The THLA-W+ was tested in 522 people living in Kor-en community located in Phuket. The scale consisted of a list of 48 words with 4 choices to test the comprehension of the meaning of the words. There were 3 methods to calculate the scores for THLA-W+: 1) the numbers of words with correct pronunciation from reading test (THLA-W+R), 2. the number of words with correct choice selection from comprehension test (THLA-W+C), and 3. the number of words with correct pronunciation and choice selection (THLA-W+RC). Reliability was tested using Cronbach’s alpha. Validity was tested by comparing the difference in THLA-W + scores between subjects with different educational levels, determining the correlation between THLA-W + and reading ability, understanding of health documents, self-assessment of reading ability, score from the screening test of those with inadequate HL and the THLA-N8 (Thai Health Literacy Assessment: Nutrition Label). The ability of THLA-W + to predict HL was analyzed using analysis of receiver operating curve. Results: The THLA-W+ from 3 methods of scoring had Cronbach’s alphas of 0.80, 0.87 and 0.87, respectively, and mean scores of 45.57 ± 3.24, 31.58 ± 7.65 and 30.59 ± 7.82, respectively (full score = 48). Subjects with higher education levels had higher scores. Correlation coefficients (r) between THLA-W+ and different HL indicators were positive (r = 0.129-0.371) and statistically significant (P < 0.001). r between THLA-W+C and THLA-W+RC was 0.977. Properties of THLA-W+C such as sensitivity, specificity, accuracy, positive predictive value (PPV), negative predictive value (NPV), likelihood ratios for positive test (LR+) and likelihood ratios for negative test (LR-) were similar to THLA-W+RC, but were better than THLA-W+R. Cut-off point of THLA-W+C was < 37 indicating inadequate HL. THLA-W+C and THLA-W+RC could discriminate people with different levels of HL when using the ability to read and understanding health documents as gold standards with 77-84 percent of sensitivity, 81-83 percent of specificity, the area under the curve at 0.86-0.87, and predictive accuracy at 77-78. Conclusion: When using the scale, its score should be calculated from comprehension test only because it is more convenient to administer and having test properties similar to THLA-W+RC.  THLA-W+C could provide important information for practical use, and suitable for HL survey in general population.