To evaluate the reliability and validity of brief subjective measures of numeracy and general health literacy in the adult emergency department setting.
A convenience sample of adult emergency department patients completed subjective measures of general health literacy (Short Literacy Screening questions, SLS) and numeracy (Subjective Numeracy Scale, SNS). These patients also completed two objective tests of literacy (the Short Test of Functional Health Literacy in Adults, S-TOFHLA; and the Rapid Estimate of Adult Literacy in Medicine, REALM) and an objective test of numeracy (WRAT4).
Internal reliability of the subjective measures was assessed using Cronbach’s alpha. Construct validity of the subjective measures was assessed by correlating them against the S-TOFHLA, REALM, and WRAT4, using Spearman’s rank correlation coefficients, receiver operating characteristics (ROC) curves, and hierarchical, multiple linear regression with adjustment for patient age, gender, race, and education.
The median age of the 207 patients surveyed was 46 (interquartile range 32, 59); twenty-seven percent were African American. Sixty-one percent of patients reported their highest level of education was high school or below. As measured by the S-TOFHLA and REALM, most patients had adequate literacy levels (89% and 80%, respectively), while 44% of patients had below average numeracy skills on the WRAT4. Median SLS was 14 (IQR 12, 15) on a scale of 3 to 15; median SNS was 36 (IQR 30, 42) on a scale of 6 to 48.
The SLS and SNS had good internal reliability, with Cronbach’s alphas of 0.74 and 0.82, respectively. The SLS Spearman’s rank order correlation coefficient was 0.33 (95% confidence interval 0.20, 0.45) for the S-TOFHLA, with a standardized beta coefficient of 0.36 (p<0.05) after adjustment for patient demographics. The SLS correlation coefficient was 0.26 (95% CI 0.13, 0.38) for the REALM, with a standardized beta coefficient of 0.38 (p<0.05) after adjustment for patient demographics. The area under the curve (AUC) for the SLS ROC curves was 0.74 (95% CI 0.68, 0.80) when compared to the S-TOFHLA and 0.72 (95% CI 0.65, 0.78) when compared to the REALM. The SNS predicted numeracy well, with a correlation coefficient of 0.57 (95% CI 0.47,0.65) for the WRAT4, a standardized beta coefficient of 0.30(p<0.05) after adjustment for patient demographics, and an ROC AUC of 0.77 (95% CI of 0.70, 0.82).
The SNS and SLS are reliable, valid tests that can be used to rapidly estimate general health literacy and numeracy skill levels in adult emergency department patients. Continuing work is needed to establish their ability to predict clinical outcomes.