Relationship between patients’ knowledge and medication adherence among patients with hypertension

Figures & data

Figure 1 Histogram of hypertension knowledge scores obtained by 233 patients.

Abbreviations: HK-LS, Hypertension Knowledge-Level Scale; K-S, Kolmogorov-Smirnov test.

Table 1 Respondents’ sociodemographic characteristics in relation to their knowledge level

Nominal (qualitative) variables	Hypertension knowledge level				P-value	1 − β
	Low N=147		High N=86
	n	%	n	%
Sex					0.638	0.071
Female	76	51.7	48	55.8
Male	71	48.3	38	44.2
Education
Primary	36	24.5	27	31.4	0.254	0.171
High school	62	42.2	37	43.0	0.905	0.037
College/university	49	33.3	22	25.6	0.721	0.186
Professional activity					0.727	0.252
Active	48	32.6	36	41.9
Nonactive	99	67.4	50	58.1
Living situation
Living alone	123	83.7	13	15.1	<0.001	1.000
Living with family/partner	22	14.9	72	83.7	<0.001	1.000
Residential care institution	3	1.4	1	1.2	0.898	0.010
Age					0.945	0.054
M ± SD	62.9±15.2		63.3±14.8
Me (Q1; Q3)	64 (55; 75)		63.5 (54; 74)
Min–Max	22–90		20–90

Abbreviations: Me, mean; SD, standard deviation; M, median; Q₁, lower quartile; Q₃, upper quartile; P, confidence level; 1 − β, test power; Min, minimum; Max, maximum.

Table 2 Respondents’ clinical characteristics in relation to knowledge level

Nominal (qualitative) variables	Hypertension knowledge level				P-value	1 − β
	Low N=147		High N=86
	n	%	n	%
BP ≥140 mmHg or ≥90 mmHg	83	56.5	26	27.9	0.032	0.989
ESC hypertension grade
Normal BP	16	10.9	11	12.8	0.662	0.049
Prehypertension	26	17.7	16	18.6	0.863	0.036
Grade 1 hypertension	70	47.6	35	40.7	0.308	0.141
Grade 2 hypertension	35	23.8	24	27.9	0.488	0.083
Comorbidities
Diabetes mellitus	60	40.8	31	36.1	0.561	0.083
COPD	50	34.0	29	33.7	0.922	0.036
Ischemic heart disease	46	31.3	13	15.1	0.010	0.752
Kidney failure	34	23.1	26	30.2	0.298	0.184
Medication
ACE inhibitors	72	49.0	42	48.8	0.909	0.036
Beta-adrenolytics	25	17.0	18	20.9	0.569	0.088
Angiotensin II receptor antagonists	10	6.8	5	5.8	0.984	0.029
Thiazide diuretics	29	19.7	18	20.9	0.959	0.039
Calcium channel blockers	49	33.3	25	29.1	0.597	0.075
Treatment type
Single-agent treatment	93	63.2	56	65.1	0.959	0.043
Combination treatment	54	36.7	30	34.9
Other hypertension treatment forms	54	36.7	38	44.2	0.325	0.168
Low-sodium/DASH diet	41	27.9	26	30.2	0.817	0.049
Weight reduction	28	19.0	20	23.3	0.549	0.096
Moderate physical activity	36	24.5	23	26.7	0.821	0.048
Keeping a self-control diary	54	36.7	52	64.2	0.048	0.979
Blood pressure control daily/weekly	52	35.4	48	57.8	0.044	0.894
Own blood pressure meter	86	58.5	64	77.1	0.052	0.795
Adherence score (MMAS-8)
Low	29	19.7	7	8.1	0.019	0.596
Moderate	80	54.4	46	53.5	0.894	0.038
High	38	25.9	33	38.4	0.047	0.458
Time from hypertension diagnosis M ± SD	11.2±8.3		12.3±9.2		0.349	0.070
MMAS-8 (score) M ± SD	6.45±1.45		7.08±1.04		0.001	0.966

Note: Use of the ©MMAS is protected by US and International copyright laws. Permission for use is required. A license agreement is available from: Donald E Morisky, MMAS Research (MORISKY) 16636 159th Place SE, Renton WA 98058, [e-mail].

Abbreviations: M, median; SD, standard deviation; MMAS-8, 8-item Morisky Medication Adherence Scale; COPD, chronic obstructive pulmonary disease; BP, blood pressure; ESC, European Cardiovascular Society; ACE, angiotensin-converting enzyme; 1 − β, test power.

Table 3 Number (proportions) of correct answers to HK-LS items in the two hypertension knowledge level subgroups

Item (correct answer)	Hypertension knowledge level				P-value	1 − β
	Low N=147		High N=86
	n	%	n	%
1. High diastolic or systolic blood pressure indicates increased blood pressure (yes)	127	86.4	84	97.7	0.004	0.788
2. Increased diastolic blood pressure also indicates increased blood pressure (yes)	123	83.7	81	94.2	0.023	0.580
3. Increased blood pressure is the result of aging, so treatment is unnecessary (no)	107	72.8	80	93.0	<0.001	0.971
4. If the medication for increased blood pressure can control blood pressure, there is no need to change lifestyles (no)	78	53.1	71	82.6	<0.001	0.997
5. If individuals with increased blood pressure change their lifestyles, there is no need for treatment (no)	89	60.5	78	90.7	<0.001	0.999
6. Individuals with increased blood pressure must take their medication in a manner that makes them feel good (no)	22	15.0	22	25.6	0.068	0.447
7. Drugs for increased blood pressure must be taken every day (yes)	117	79.6	81	94.2	0.005	0.842
8. Individuals with increased blood pressure must take their medication only when they feel ill (no)	105	71.4	84	97.7	<0.001	0.999
9. Individuals with increased blood pressure must take their medication throughout their life (yes)	94	63.9	80	93.0	<0.001	0.999
10. For individuals with increased blood pressure, the best cooking method is frying (no)	98	66.7	81	94.2	<0.001	0.999
11. For individuals with increased blood pressure, the best cooking method is boiling or grilling (yes)	95	64.6	69	80.2	0.018	0.668
12. Individuals with increased blood pressure can eat salty foods as long as they take their drugs regularly (no)	48	32.7	63	73.3	<0.001	1.000
13. Individuals with increased blood pressure must eat fruits and vegetables frequently (yes)	70	47.6	76	88.4	<0.001	1.000
14. The best type of meat for individuals with increased blood pressure is red meat (no)	26	17.7	50	58.1	<0.001	1.000
15. The best type of meat for individuals with increased blood pressure is white meat (yes)	46	31.3	64	74.4	<0.001	1.000
16. Individuals with increased blood pressure must not smoke (yes)	74	50.3	70	81.4	<0.001	0.998
17. Individuals with increased blood pressure can drink alcoholic beverages (no)	110	74.8	81	94.2	<0.001	0.970
18. Increased blood pressure can cause strokes, if left untreated (yes)	125	85.0	86	100.0	<0.001	0.984
19. Increased blood pressure can cause heart diseases, such as heart attack, if left untreated (yes)	125	85.0	85	98.8	<0.001	0.940
20. Increased blood pressure can cause premature death if left untreated (yes)	126	85.7	86	100.0	<0.001	0.977
21. Increased blood pressure can cause kidney failure, if left untreated (yes)	111	75.5	85	98.8	<0.001	0.999
22. Increased blood pressure can cause visual disturbances, if left untreated (yes)	108	73.5	82	95.3	<0.001	0.993
HK-LS questionnaire domains (M ± SD)	Low N=147		High N=86		P-value	1 − β
Definition	1.70±0.65		1.92±0.28		0.012	0.948
Treatment	2.30±1.01		3.10±0.55		<0.001	1.000
Drug adherence	2.19±1.14		3.40±0.69		<0.001	1.000
Lifestyle	3.04±1.15		4.48±0.64		<0.001	1.000
Diet	0.49±0.64		1.33±0.73		<0.001	1.000
Complications	4.05±1.46		4.93±0.26		<0.001	1.000
Total score (M ± SD)	13.8±3.7		19.1±1.1		<0.001	1.000

Abbreviations: HK-LS, Hypertension Knowledge-Level Scale; M, median; SD, standard deviation; P, significance level; 1 − β, test power.

Figure 2 Comparison of correct answer proportions for each HK-LS item in the two groups differentiated by their level of knowledge on hypertension (items with <50% correct answers are marked in red).

Abbreviation: HK-LS, Hypertension Knowledge-Level Scale.

Figure 3 Comparison of correct answer percentages in the 6 HK-LS domains between the two groups differentiated by their level of knowledge on hypertension.

Abbreviation: HK-LS, Hypertension Knowledge-Level Scale.

Table 4 Proportions of correct answers in HK-LS domains for the two subgroups

Domain	Total (%)	Group 1 (%) N=147	Group 2 (%) N=86	1 vs 2 P-value	1 − β
Definition	89.1	85.0	95.9	0.012	0.676
Treatment	65.9	57.5	77.6	<0.001	0.857
Drug adherence	65.9	54.8	84.9	<0.001	0.998
Lifestyle	70.7	60.8	87.7	<0.001	0.995
Diet	39.9	24.5	66.3	<0.001	1.000
Complications	87.5	81.0	98.6	<0.001	0.988
Total	71.5	62.6	86.6	<0.001

Abbreviations: HK-LS, Hypertension Knowledge-Level Scale; 1 − β, test power.

Table 5 Single- and multiple-factor regression analysis results for the variables studied against MMAS scores

Nominal (qualitative) variables	Single-factor analysis		Multiple-factor analysis
	ρ/F (95% CI)	P-value	b	P-value
Age, years	0.019 (−0.106 to 0.146)	0.772	–	–
Female sex	0.028 (−0.028 to 0.155)	0.671	–	–
Education	0.107 (−0.016 to 0.232)	0.104	–	–
Professional activity – active	−0.012 (−0.137 to 0.116)	0.861	–	–
Living situation – living alone	−0.080 (−0.206 to 0.050)	0.222	–	–
ESC hypertension grade	0.082 (−0.041 to 0.208)	0.212	–	–
Duration of hypertension in years	−0.013 (−0.138 to 0.115)	0.848	–	–
Regular BP measurements	0.171 (0.049 to 0.294)	0.009	0.183 (0.051 to 0.296)	0.004
Diary of self-control	0.177 (0.055 to 0.300)	0.007	0.115 (−0.008 to 0.240)	0.089
Concurrent non-pharmaceutical treatment	0.182 (0.060 to 0.305)	0.006	0.171 (0.049 to 0.294)	0.006
Ischemic heart disease	−0.184 (−0.065 to 0.3070)	0.005	−0.199 (−0.068 to 0.2980)	0.001
High level of knowledge on hypertension (HK-LS)	0.173 (0.051 to 0.296)	0.008	0.208 (0.087 to 0.330)	0.001

Note: Use of the © MMAS is protected by US copyright laws. Permission for use is required. A license agreement is available from: Donald E. Morisky, ScD, ScM, MSPH, Professor, Department of Community Health Sciences, UCLA School of Public Health, 650 Charles E. Young Drive South, Los Angeles, CA 90095-1772.

Abbreviations: MMAS, Morisky Medication Adherence Scale; ESC, European Society of Cardiology; BP, blood pressure; HK-LS, Hypertension Knowledge-Level Scale.

Table 6 Spearman’s rank correlation coefficients (ρ) and significance values (P) for correlations between HK-LS domains and MMAS-8 scores

Subdimension	Total	Low knowledge level	High knowledge level
	N=233	N=147	N=86
Definition	ρ=0.110	ρ=0.062	ρ=0.181
	P=0.094	P=0.451	P=0.095
Medical treatment	ρ=0.079	ρ=0.028	ρ=0.024
	P=0.230	P=0.732	P=0.826
Drug adherence	ρ=0.242	ρ=0.303	ρ=0.029
	P<0.001	P<0.001	P=0.789
Lifestyle	ρ=0.065	ρ=−0.022	ρ=−0.021
	P=0.320	P=0.788	P=0.845
Diet	ρ=0.058	ρ=−0.024	ρ=0.013
	P=0.378	P=0.771	P=0.901
Complications	ρ=0.068	ρ=0.061	ρ=−0.140
	P=0.301	P=0.458	P=0.197
Total score	ρ=0.179	ρ=0.151	ρ=0.028
	P=0.007	P=0.068	P=0.799

Note: Use of the © MMAS is protected by US copyright laws. Permission for use is required. A license agreement is available from: Donald E. Morisky, ScD, ScM, MSPH, Professor, Department of Community Health Sciences, UCLA School of Public Health, 650 Charles E. Young Drive South, Los Angeles, CA 90095-1772.

Abbreviations: HK-LS, Hypertension Knowledge-Level Scale; MMAS-8, 8-item Morisky Medication Adherence Scale.