Is health literacy an example of construct proliferation? A conceptual and empirical evaluation of its redundancy with general cognitive ability

During the last 20 years, health literacy has been promoted as an important determinant of individual and group differences in health outcomes. Despite a definition and pattern of associations with health outcomes highly similar to 'g' (i.e., the general cognitive ability factor), health literacy has been conceptualized as a distinct construct. This study evaluates the conceptual and empirical distinctiveness of health literacy. A sample of 167 students from a southeastern urban university (117 females and 50 males) between the ages of 18 and 53 (M = 21.31, SD = 5.61) completed a cognitive ability battery, three health literacy tests, two knowledge tests, and a questionnaire assessing 12 health behaviors and health outcomes. Across 36 tests of criterion-related validity, cognitive ability had an effect in all 36 cases, where the health literacy tests only showed measureable incremental validity in 6 of 36 cases. Factor analysis revealed only three factors defined by the traditional ability tests with the health literacy measures loading on the ability factors as predicted by the content validity analysis. There was no evidence of a health literacy factor. The combined results from a comparative content analysis, an empirical factor analysis, and an incremental validity analysis cast doubt on the uniqueness of a health literacy construct. It is suggested that measures of health literacy are simply domain-specific contextualized measures of basic cognitive abilities. Implications for linking these literatures and increasing our understanding of the influence of intellectual factors on health are discussed.