Table 1. Difference in means.

The data source is the universe of birth certificates in Pennsylvania (2004–2013) matched to the Pennsylvania DEP Internal Operator Well Inventory. Maternal and infant demographic indicators and health outcomes are recorded at the time of birth. “Near, 0–1 km” indicates that the mother lives within 0 to 1 km of at least one well site. “Far, 3–15 km” indicates that the mother lives 3 to 15 km from the nearest well site. Columns (5) to (7) report P values from t tests of equality of means across the different samples indicated. Column (7) tests whether (2) − (1) = (4) − (3). This quantity is referred to as the difference-in-differences, or D-in-D.

Near, 0–1 kmFar, 3–15 kmP values
BeforeAfterBeforeAfter(5)(6)(7)
(1)(2)(3)(4)(1) − (2)(3) − (4)D-in-D
Mother characteristics
Married0.680.610.620.630.000.000.00
Black0.010.020.120.060.010.000.00
Hispanic0.010.010.020.020.660.000.57
<High school0.110.120.110.100.270.000.01
High school0.280.310.260.250.020.000.00
Some college0.320.320.280.290.890.000.43
College0.220.170.220.230.000.000.00
Advanced0.080.080.130.130.740.690.74
<20 years old0.060.060.060.050.890.000.11
20–24
years old
0.210.260.220.210.000.000.00
25–29
years old
0.300.310.290.290.420.000.86
30–34
years old
0.260.230.270.280.010.000.00
>35 years old0.170.140.170.160.010.000.07
Infant characteristics
Male0.500.520.510.520.240.270.32
First born0.420.410.430.430.660.150.84
Second born0.330.340.330.330.460.050.68
Third born0.160.160.150.150.790.640.73
Fourth and up0.090.090.090.090.900.510.98
Health outcomes
Low birth
weight
0.050.070.060.060.040.000.01
Birth weight3354.353312.813316.943331.080.010.000.00
Health index0.050.010.010.020.010.000.00
n48711798133,10778,366