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Table 2 Standardised Differences across Covariates: before Matching and after Matching

From: Association between intimate partner violence during pregnancy and risk of preterm birth

 

Before matching

After matching

IPV

No IPV

p-value

%bias

IPV

No IPV

p-value

%bias

Age (Years)

 20–24

14.6

22.8

0.05

−21.1

14.6

17.3

0.596

−7

 25–29

24.3

26.4

0.635

−4.8

24.3

25.0

0.898

−1.8

 30–34

24.3

24.1

0.968

0.4

24.3

21.2

0.597

7.2

 35–39

20.4

13.4

0.041

18.7

20.4

20.8

0.945

−1

 40–44

6.8

6.4

0.884

1.4

6.8

6.2

0.866

2.3

 45–49

2.9

1.2

0.135

11.8

2.9

2.5

0.865

2.7

Level of Education

 Primary

26.2

28.7

0.578

−5.6

26.2

20.6

0.342

12.6

 Secondary plus

73.8

71.3

0.578

5.6

73.8

79.4

0.342

−12.6

Husbands’ level of education

 Primary

17.5

19.8

0.565

−5.9

17.5

16.3

0.824

3

 Secondary plus

81.6

79.1

0.546

6.1

81.6

83.1

0.771

−3.9

Wealth Index

 Middle

11.7

15.4

0.297

−11

11.7

14.0

0.619

−6.8

 Rich

63.1

47.5

0.002

31.7

63.1

62.7

0.954

0.8

Work status

 Not working

51.5

49.3

0.67

4.2

51.5

53.0

0.824

−3.1

Residence

 Urban

43.7

61.6

0

−36.4

43.7

41.7

0.779

3.9

Smoke

 Cigarette smoking

1.0

0.1

0.032

11.3

1.0

1.2

0.893

−2.6

Age at first intercourse

 15–17

33.0

39.9

0.156

−14.4

33.0

30.7

0.721

4.8

 18+

63.1

54.8

0.093

17

63.1

66.4

0.622

−6.7

Prenatal Care

93.2

94.5

0.577

−5.3

93.2

93.8

0.866

−2.4

Number of antenatal visits

 4–7 times

34.0

48.4

0.004

−29.5

34.0

36.5

0.706

−5.2

 8–20 times

16.5

12.5

0.228

11.3

16.5

14.8

0.731

5

Wanted pregnancy

62.1

68.9

0.143

−14.2

62.1

61.9

0.977

0.4

  1. *The standardised percentage bias. The standardised % bias is the % difference of the sample means in the treatment and control (full or matched) sub-samples as a percentage of the square root of the average of the sample variances in the treated and non-treated groups [30]