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Table 1 Comparison of Covariate Balance between NSAIDs and Acetaminophen before and after propensity score matching

From: Comparative effects of non-steroidal anti-inflammatory drugs (NSAIDs) on blood pressure in patients with hypertension

Variable

Sample

NSAIDs*

Acetaminophen*

P Value**

Standardized Difference

Bias Reduction (%)

Age (yrs) mean

Unmatched

55

60

<.001

−42.0

 
 

Matched

56

57

0.119

−6.0

86%

Gender:

      

Female

Unmatched

70

70

0.687

1.3

 
 

Matched

72

70

0.157

5.5

−323%

Race:

      

African American

Unmatched

58

63

0.003

−9.4

 
 

Matched

63

61

0.353

3.6

62%

Other

Unmatched

5

3

0.007

7.5

 
 

Matched

4

3

0.837

0.8

89%

Baseline systolic blood pressure (mmHg) mean

Unmatched

139

141

0.006

−8.8

 
 

Matched

140

140

0.949

−0.2

97%

Time from baseline SBP to index:

      

≤ 7 days

Unmatched

53

65

<.001

−23.8

 
 

Matched

62

61

0.596

2.0

91%

> 7 days and ≤ 30 days

Unmatched

14

10

<.001

11.6

 
 

Matched

10

11

0.380

−3.4

71%

> 30 days

Unmatched

33

25

<.001

17.4

 
 

Matched

28

28

0.975

0.1

99%

Year of index date:

      

1993 - 1996

Unmatched

50

58

<.001

−17.1

 
 

Matched

57

56

0.713

1.4

92%

1997-2002

Unmatched

39

40

0.477

−2.3

 
 

Matched

41

42

0.741

−1.3

44%

2003 - 2006

Unmatched

11

1

<.001

40.8

 
 

Matched

2

2

0.881

−0.6

99%

Diagnosis of:

      

Osteoarthritis

Unmatched

22

23

0.768

−0.9

 
 

Matched

21

22

0.295

−4.0

−327%

Rheumatoid Arthritis

Unmatched

3

3

0.381

2.8

 
 

Matched

3

3

0.819

0.9

69%

Renal Insufficiency

Unmatched

3

8

<.001

−24.5

 
 

Matched

4

4

0.922

0.4

98%

Cirrhosis with Ascites

Unmatched

0.4

1

0.343

−3.0

 
 

Matched

1

1

0.807

−0.9

69%

Systemic Lupus Erythematosus

Unmatched

1

1

0.277

3.5

 
 

Matched

1

1

0.465

−2.8

20%

Diabetes

Unmatched

28

35

<.001

−14

 
 

Matched

28

31

0.124

−5.9

58%

Congestive Heart Failure

Unmatched

11

19

<.001

−20.9

 
 

Matched

14

14

0.651

−1.7

92%

Coronary Artery Disease or History of Myocardial Infarction

Unmatched

13

19

<.001

−16.0

 
 

Matched

14

15

0.266

−4.3

73%

Stroke

Unmatched

8

12

<.001

−15.4

 
 

Matched

9

9

0.784

−1.1

93%

Arrhythmia

Unmatched

1

2

0.055

−6.1

 
 

Matched

1

1

0.489

−2.7

56%

Asthma or Chronic Obstructive Pulmonary Disease

Unmatched

17

19

0.121

−5.0

 
 

Matched

18

19

0.420

−3.1

37%

Medications:

      

ACE-I or Angiotensin II blocker

Unmatched

36

43

<.001

−15.7

 
 

Matched

37

38

0.594

−2.1

87%

Beta- Blocker

Unmatched

18

17

0.270

3.5

 
 

Matched

15

17

0.338

−3.7

−4%

Calcium Channel Blocker

Unmatched

34

38

0.003

−9.7

 
 

Matched

36

36

0.829

−0.8

91%

Diuretic

Unmatched

44

48

0.005

−9.0

 
 

Matched

46

45

0.921

0.4

96%

Other BP medications

Unmatched

7

12

<.001

−15.2

 
 

Matched

9

9

0.835

−0.8

95%

Oral high dose glucocorticoid***

Unmatched

1

1

0.068

−5.8

 
 

Matched

1

1

0.850

−0.7

87%

Oral Contraceptives

Unmatched

1

1

0.528

−2.0

 
 

Matched

1

1

0.998

0.0

100%

Venlafaxine

Unmatched

1

0.3

0.075

5.8

 
 

Matched

1

0.4

0.782

1.1

82%

Adherence to antihypertensive medications:

      

MPR ≥ 80%

Unmatched

69

74

<.001

−10.6

 
 

Matched

72

70

0.320

3.8

64%

MPR < 80%

Unmatched

13

12

0.262

3.6

 
 

Matched

12

13

0.159

−5.4

−51%

Not using antihypertensives (reference group)

Unmatched

18

14

0.002

9.8

 
 

Matched

16

16

0.965

0.2

98%

Exposure to index drug:

      

MPR > 80%

Unmatched

32

24

<.001

19.5

 
 

Matched

26

27

0.750

−1.2

94%

MPR 20–80 %

Unmatched

44

43

0.278

3.5

 
 

Matched

44

43

0.859

0.7

80%

MPR < 20%

Unmatched

23

34

<.001

−23.3

 
 

Matched

30

30

0.909

0.4

98%

Number of refills per month:

      

≥ 1 refills

Unmatched

52

36

<.001

30.8

 
 

Matched

44

43

0.301

4.0

87%

  1. * % unless indicated as mean. Because of rounding values may not add to 100 %.
  2. ** P-value of t-tests for continuous variables and chi-square tests for categorical variables.
  3. *** High dose was defined as ≥10mg for prednisonse, ≥50mg for cortisone, and ≥1.5 mg for dexamethasone.
  4. Standardized difference: 100 ( χ ¯ treated – χ ¯ control)/√ {(s2 treated + s2 control)/2}. A positive value means the treated group is higher in % (or mean) compared to the control group and negative value means the control is higher than the treated.
  5. Bias reduction (%) =1- {|Standardized difference matched|/| Standardized difference unmatched |} x 100. A positive value means bias is reduced by propensity score matching and negative means bias increased.
  6. ACE-I: Angiotensin converting enzyme inhibitor; MPR: Medication Possession Ratio; SBP: Systolic blood pressure. Unmatched: all patients before propensity score matching, N=3,928 (2,181 NSAIDs and 1,747 acetaminophen). Matched: only matched patients, N=2,680 (1,340 in each group).
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BMC Cardiovascular Disorders

ISSN: 1471-2261

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