Health Literacy, Education, and Internal Consistency of Psychological Scales

BACKGROUND: Measurement error might lead to biased estimates, causing ineffective interventions and service delivery. Identifying measurement error of health-related instruments helps develop accurate assessment of health-related constructs. OBJECTIVE: We compared the internal consistency of eight psychological scales used in health research in groups with adequate versus limited health literacy and in groups with higher versus lower education. METHODS: Participants (N = 1,005) from a nationally representative internet panel completed eight self-report scales: (1) information avoidance, (2) cognitive causation, (3) unpredictability, (4) perceived severity, (5) time orientation, (6) internal health locus of control, (7) need for cognition, and (8) social desirability. The first four assess beliefs about diabetes and colon cancer. We used the Newest Vital Sign to categorize participants' health literacy (limited vs. adequate). We also categorized participants' education (high school or less vs. more than high school). We compared the Cronbach's alpha for each psychological scale between groups with different health literacy and education levels using the Feldt test. KEY RESULTS: Among all the 13 subscales, scale internal consistency was significantly lower among people with limited health literacy than those with adequate health literacy for five subscales: information avoidance for colon cancer (0.80 vs. 0.88), unpredictability of diabetes (0.84 vs. 0.88), perceived severity for diabetes (0.66 vs. 0.75), need for cognition (0.63 vs. 0.82), and social desirability (0.52 vs. 0.68). Internal consistency was significantly lower among people who had a high school education or less than among those with more than a high school education for four scales: perceived severity of diabetes (0.70 vs. 0.75), present orientation (0.60 vs. 0.66), need for cognition (0.73 vs. 0.80), and social desirability (0.61 vs. 0.70). CONCLUSIONS: Several psychological instruments demonstrated significantly lower internal consistency when used in a sample with limited health literacy or education. To advance health disparities research, we need to develop new scales with alternative conceptualizations of the constructs to produce a measure that is reliable among multiple populations. [HLRP: Health Literacy Research and Practice. 2021;5(3):e244–e255.] PLAIN LANGUAGE SUMMARY: We compared the internal consistency of several psychological scales in groups with adequate versus limited health literacy and higher versus lower education. For several scales, internal consistency was significantly lower among (1) people with limited health literacy compared those who have adequate health literacy and/or (2) people who had a high school education or less compared to those with more than a high school education.