Background: Health literacy and numeracy influence many health-related behaviors and outcomes. Health literacy and numeracy have been assessed objectively and subjectively, but interrelationships among the measures and the consistency of their association with health knowledge have not been examined.
Objective: To increase understanding of the structure and interrelations among objective and subjective health literacy and numeracy and how these constructs relate to knowledge of risk factors of two major diseases.
Design: Secondary analysis of cross-sectional survey data, weighted to be representative of the general US population of non-institutionalized adults.
Participants: Participants (N = 1005, 55.2% response rate) were recruited from GfK KnowledgePanel. The unweighted sample included 52% women, 26% racial/ethnic minorities, and 37% with no college experience.
Main measures: Objective health literacy, subjective health literacy, objective numeracy, subjective numeracy. Objective and perceived knowledge of diabetes and colon cancer risk factors were also assessed.
Key results: Confirmatory factor analyses indicated that a model with correlated (r = 0.16-0.56) but separate factors for each of the four literacy/numeracy constructs best fit the data (RMSEA = 0.055 (95% CI 0.049-0.061), CFI = 0.94). Consistency between measures in classifying people as having adequate or limited health literacy or numeracy was 60.9-77.1%, depending on the combination of measures. All four literacy/numeracy constructs were independently associated with objective diabetes knowledge and objective colon cancer knowledge (all ps < .04). Subjective (but not objective) literacy and numeracy measures were associated with diabetes perceived knowledge (all ps < .02). No literacy/numeracy measures were associated with perceived colon cancer knowledge.
Conclusions: We identified objective and subjective health literacy and numeracy as four distinct but related concepts. We also found that each construct accounts for unique variance in objective (but not subjective) disease knowledge. Until research uncovers what psychological processes drive subjective measures (e.g., motivation, self-efficacy), research investigating the relationship between health literacy and health outcomes should consider assessing all four measures.
Keywords: colon cancer; diabetes; health literacy; knowledge; numeracy.