Table 8 Mean values of the covariates before and after the matching (caliper matching)

Variable

Sample

Treated

Control

%bias

%|bias| reduction

t

p > |t|

Age

Unmatched

30.76

30.78

−0.40

− 0.76

0.45

Matched

30.76

30.74

0.60

−47.50

1.39

0.17

Age square

Unmatched

959.80

965.90

−2.40

−4.70

<0.001

Matched

959.80

958.30

0.60

74.50

1.48

0.14

Migrant

Unmatched

0.33

0.49

−31.40

−61.24

<0.001

Matched

0.33

0.34

−0.80

97.60

−1.77

0.08

Gravidity

Unmatched

1.73

1.97

−21.20

−41.98

<0.001

Matched

1.73

1.73

0.50

97.40

1.37

0.17

Parity

Unmatched

1.22

1.32

−19.90

−39.27

<0.001

Matched

1.22

1.22

0.30

98.40

0.78

0.43

Employed

Unmatched

0.98

0.89

35.70

75.45

<0.001

Matched

0.98

0.98

0.01

100.00

−0.06

0.95

Ethnic status

Unmatched

0.99

0.99

1.10

2.05

0.04

Matched

0.99

0.99

−1.20

−17.20

−2.93

<0.001

Nationality

Unmatched

1.00

0.99

10.70

23.92

<0.001

Matched

1.00

1.00

0.01

99.70

0.58

0.56

Marriage status

Unmatched

1.00

1.00

5.90

12.33

<0.001

Matched

1.00

1.00

−0.40

92.70

−1.62

0.11

High-risk pregnancy

Unmatched

0.55

0.60

−11.00

−21.30

<0.001

Matched

0.55

0.55

−0.40

96.70

−0.80

0.42

Pregnancy complications

Unmatched

0.14

0.16

−7.90

−15.52

<0.001

Matched

0.14

0.13

0.40

94.90

0.95

0.34

Any condition (gestational diabetes, hypertension, anemia)

Unmatched

0.09

0.13

−12.60

−24.80

<0.001

Matched

0.09

0.09

0.80

93.70

1.94

0.05