Association of Health Literacy With Medication Knowledge, Adherence, and Adverse Drug Events Among Elderly Veterans

Figures & data

Table 1. Patient characteristics and medication knowledge, adherence, and safety (N = 310)

Variable	n
Demographics
Age in years, M (SD)	73.9 (5.3)
White, n (%)	306 (99.0%)
Men, n (%)	301 (97.1%)
Education
Completed grade school	94 (30.3%)
Completed high school	128 (41.3%)
Beyond high school	88 (28.4%)
Health literacy, Rapid Estimate of Adult Literacy in Medicine score, M (SD)	58.2 (10.3)
Low (≤6th-grade equivalent), n (%)	27 (8.7%)
Marginal (7th–8th-grade equivalent), n (%)	94 (30.3%)
Adequate (≥9th-grade equivalent), n (%)	189 (61.0%)
Functional status
Cognition, Short Portable Mental Status Questionnaire baseline score, M (SD)	0.5 (0.8)
Modified Older Americans Resources and Services Activities of Daily Living baseline score, M (SD)	13.2 (1.7)
Activities of daily living item: take medications in the correct amounts and at the correct times
Unable, n (%)	0 (0%)
Some help, n (%)	22 (7.1%)
No help/on own, n (%)	288 (92.9%)
Medication knowledge
% of medication names known per patient at baseline, M	56.4%
% of medication purpose known per patient at baseline, M	78.5%
Medication adherence
% of medications taken according to label at baseline, M	71.4%
Refill-based adherence (medication possession ratio), year before baseline, M	0.92
Refill-based adherence (medication possession ratio), year after baseline, M	0.89
Number of medications
No. of medications at baseline, M (SD)	13.2 (4.7)
No. of medications at 12 months, M (SD)	13.6 (4.4)
Medication safety and outcomes
Adverse drug event within 3 months after baseline, n (%)	51 (16.5%)
Adverse drug event within 12 months after baseline, n (%)	119 (38.4%)

Table 2. Patient characteristics and medication knowledge, adherence, and safety, stratified by health literacy groupings

	Health Literacy (Rapid Estimate of Adult Literacy in Medicine groupings)			Comparisons
Variable	Group 1: Low n = 27	Group 2: Marginal n = 94	Group 3: Adequate n = 189	Group 1 vs. 2 and 3 F or χ^2; df; p	Group 3 vs. 1 and 2 F or χ^2; df; p
Demographics
Age in years, M (SD)	73.2 (5.4)	73.9 (5.5)	74.0 (5.2)	0.51; 1; .48	0.42; 1; .52
Education, n (%)
Grade school (n = 94)	22 (23.4%)	41 (43.6%)	31 (33.0%)	37; 2; < .001	48; 2; < .001
High school (n = 128)	4 (3.1%)	37 (29.0%)	87 (68.0%)
Beyond high school (n = 88)	1 (1.1%)	16 (18.2%)	71 (80.7%)
Medication knowledge
% of medication names known, baseline	32.2%	54.6%	60.8%	10.9; 1; .001	14.1; 1; < .001
% of medication purposes known, baseline	61.8%	77.4%	81.4%	13.9; 1; < .001	16.8; 1; < .001
Medication adherence
% of medication taken according to label, baseline	73.8%	73.0%	70.4%	0.85; 1; .36	0.91; 1; .34
Medication possession ratio, year before baseline, M	0.904	0.922	0.921	0.15; 1; .70	0.00; 1; .96
Medication possession ratio, year after baseline, M	0.880	0.898	0.892	0.33; 1; .57	0.12; 1; .73
Medication safety and outcomes No. of medications at baseline, M (SD)	12.9 (5.0)	13.1 (5.3)	13.4 (4.3)	0.14; 1; .71	0.37; 1; .54
Adverse drug event
Within 3 months after baseline (%)	7 (25.9%)	11 (11.7%)	33 (17.5%)	1.9; 1; .16	0.36; 1; .55
Within 12 months after baseline (%)	13 (48.1%)	31 (33.0%)	75 (39.7%)	1.2; 1; .28	0.34; 1; .56

Table 3. Multivariable models of adverse drug event risk at 12 months: Health literacy versus education

	Model 1: Health literacy	Model 2: Education	Model 3: Both
Health literacy
Low	1.6 (0.65, 3.7) p = .32	—	1.8 (0.69, 4.6) p = .23
Marginal	0.73 (0.43, 1.2) p = .24	—	0.77 (0.44, 1.3) p = .35
Adequate	—	—	—
Education
Grade school	—	0.91 (0.48, 1.7) p = .76	0.86 (0.43, 1.7) p = .66
High school	—	1.1 (0.63, 2.0) p = .72	1.1 (0.64, 2.0) p = .67
Beyond high school	—	—	—