Association of health literacy and medication self-efficacy with medication adherence and diabetes control

Figures & data

Table 1 Descriptive statistics of the study participants (n = 174)

Variables	n (%)	Mean (SD)
Age (years)		58.7 (12.8)
Gender
Female	100 (57.5)
Male	74 (42.5)
Race
White	118 (67.8)
Black	43 (24.7)
Hispanic	8 (4.6)
Asian	4 (2.3)
American Indian	1 (0.6)
Education
Completed eighth grade or less	4 (2.3)
Some high school	15 (8.6)
High school graduate or GED	47 (27.0)
Some college or technical school	67 (38.5)
College graduate	24 (13.8)
Graduate degree	17 (9.8)
Having health insurance	174 (100.0)
Annual household income
Less than US ≥20,000	74 (42.5)
Equal or more than US ≥20,000	100 (57.5)
Number of medications		7.8 (3.9)
Number of illnesses		3.9 (1.8)
Frequency of medication use
Once daily	17 (9.8)
Twice daily	81 (46.6)
Three times daily	56 (32.2)
Four times daily	20 (11.5)
Insulin use
Yes	64 (36.8)
No	110 (63.2)
Self-rated health status
Poor	12 (6.9)
Fair	61 (35.1)
Good	79 (45.4)
Very good	21 (12.1)
Excellent	1 (0.6)
Duration of diabetes diagnosed (years)		9.6 (7.1)
HbA1c level (%)a		7.7 (1.6)
≤7% (53.0 mmol/mol)	77 (44.3)
>7% (53.0 mmol/mol)	96 (55.2)
Missing	1 (0.6)
Health literacy		3.7 (2.0)
Inadequate (score = 0–1)	31 (17.8)
Marginal (score = 2–3)	39 (22.4)
Adequate (score = 4–6)	104 (59.8)
Medication self-efficacy (score = 13–39)		33.2 (6.0)
Self-reported diabetes medication adherenceb		5.9 (1.9)
Low (score <6)	71 (40.8)
Medium (score 6 to <8)	61 (35.1)
High (score 8)	42 (24.1)

Notes:

a The mean HbA1c value of 7.7% is equal to 60.7 mmol/mol.

b Use of the ©MMAS is protected by US Copyright laws. Permission for use is required. A license agreement is available from: Donald E Morisky, MMAS Research LLC 14725 NE 20th St. Bellevue WA 98007 or from [e-mail].

Abbreviations: GED, general equivalency development (or general equivalency diploma); SD, standard deviation.

Table 2 Spearman rho correlations of diabetes medication adherence, HbA1c, and other covariates

Variables	Age	Gender	Race	Education	Income	NM	NI	HS	YDM	FM	Insulin use	HL	SE	MA	HbA1c
Age	1.00
Gender	0.04	1.00
Race	−0.37***	−0.04	1.00
Education	0.02	0.03	−0.02	1.00
Income	0.24**	0.22**	−0.30***	0.37***	1.00
NM	0.15*	−0.04	−0.11	0.02	−0.14	1.00
NI	0.23**	−0.03	−0.13	−0.02	−0.08	0.76***	1.00
HS	0.19*	0.21**	−0.12	0.21**	0.31***	−0.38***	−0.35***	1.00
YDM	0.25**	0.14	−0.14	−0.03	0.03	0.22**	0.13	−0.06	1.00
FM	0.12	0.03	−0.07	−0.10	−0.12	0.51***	0.46***	−0.20*	0.28***	1.00
Insulin use	−0.04	0.12	0.04	−0.05	−0.12	0.36***	0.23**	−0.17*	0.28***	0.26**	1.00
HL	−0.02	−0.02	−0.34***	0.44***	0.42***	0.02	0.02	0.12	0.04	−0.03	−0.10	1.00
SE	0.27***	0.20**	−0.27***	0.05	0.28***	−0.05	−0.04	0.22**	0.03	0.11	−0.05	0.13	1.00
MA	0.28***	0.15*	−0.24**	0.03	0.24**	−0.02	0.05	0.29***	−0.02	0.14	−0.05	0.12	0.63***	1.00
HbA1c	−0.14	0.11	0.15*	−0.01	−0.08	0.10	−0.00	−0.09	0.04	−0.01	0.39***	−0.06	−0.08	−0.24**	1.00

Note:

* p < 0.05,

** p < 0.01,

*** p < 0.001.

Abbreviations: NM, the number of prescription medicines; NI, the number of illnesses; HS, health status; YDM, the years of diabetes; FM, the frequency of the daily medicines; HL, health literacy; SE, medication self-efficacy; MA, diabetes medication adherence.

Table 3 Multiple linear regression: diabetes medication adherence regressed on demographics, diabetes- and health-related factors, health literacy, and medication self-efficacy (n = 174)

Dependent variable: diabetes medication adherence
Independent variables	B	SE	β	p-value
Demographic factors
Age	0.01	0.01	0.04	0.581
Male	0.04	0.24	0.01	0.858
Non-whitea	−0.28	0.29	−0.07	0.330
Highest education degree more than high school levelb	0.06	0.27	0.01	0.837
Annual household incomec	0.23	0.28	0.06	0.422
Diabetes- and health-related factors
Number of medications	−0.02	0.04	−0.04	0.678
Number of illnesses	0.14	0.09	0.14	0.123
Health statusd	0.65	0.26	0.17	0.015
Duration of diagnosed diabetes (years)	−0.01	0.02	−0.03	0.661
Health literacy	−0.04	0.07	−0.04	0.586
Medication self-efficacy	0.17	0.02	0.53	<0.001
F	10.95***
R^2	42.7%

Notes:

*** p < 0.001.

a Compared with white patients.

b Compared with those with highest education degree less than some college or technical school.

c Measured at the annual household income of US ≥20,000.

d Compared with poor or fair health status reported. The values in bold font show statistical significance (p < 0.05).

Abbreviations: B, unstandardized coefficient; SE, standard error; β, standardized coefficient.

Table 4 Multiple linear regression: HbA1c regressed on demographics, diabetes- and health-related factors, health literacy, medication self-efficacy, and diabetes medication adherence (n = 174)

Dependent variable: HbA1c	Model 1				Model 2
Independent variables	B	SE	β	p-value	B	SE	β	p-value
Demographic factors
Age	−0.02	0.01	−0.17	0.061	−0.02	0.01	−0.16	0.074
Male	0.41	0.26	0.12	0.118	0.42	0.28	0.13	0.105
Non-whitea	0.28	0.32	0.08	0.379	0.22	0.31	0.06	0.486
Highest education degree more than high school levelb	−0.42	0.29	−0.12	0.154	−0.41	0.29	−0.12	0.156
Annual household incomec	0.26	0.31	0.08	0.403	0.31	0.30	0.09	0.309
Diabetes- and health-related factors
Number of medications	0.12	0.05	0.29	0.009	0.12	0.05	0.28	0.009
Number of illnesses	−0.12	0.10	−0.14	0.226	−0.09	0.10	−0.10	0.365
Health statusd	−0.02	0.29	−0.01	0.953	0.13	0.29	0.04	0.653
Duration of diabetes diagnosed (years)	0.01	0.02	0.04	0.590	0.01	0.02	0.04	0.644
Health literacy	−0.04	0.08	−0.05	0.621	−0.05	0.08	−0.06	0.542
Medication self-efficacy	−0.02	0.02	−0.08	0.305	0.02	0.03	0.05	0.566
Diabetes medication adherence					−0.23	0.09	−0.26	0.008
F	2.00*				2.51**
R^2	12.0%				15.7%

Notes: Model 1 did not include diabetes medication adherence in the regression, but Model 2 included diabetes medication adherence as a covariate in the regression.

* p < 0.05,

** p < 0.01.

a Compared with white patients.

b Compared with those with highest education degree less than college or technical school.

c Measured at the annual household income of US ≥20,000.

d Compared with poor or fair self-reported health status. The values in bold font show statistical significance (p < 0.05).

Abbreviations: B, unstandardized coefficient; SE, standard error; β, standardized coefficient.

Figure S1 Conceptual framework of the association of health literacy, medication self-efficacy, diabetes medication adherence, HbA1c, and the covariates based on the literature review.