|
Variable
|
Midwesta (n = 8869)
|
Northeasta (n = 6572)
|
Southa (n = 14,452)
|
Westa (n = 9573)
|
|---|
|
Percent Change (95% CI)
|
p-value
|
Percent Change (95% CI)
|
p-value
|
Percent Change (95% CI)
|
p-value
|
Percent Change (95% CI)
|
p-value
|
|---|
|
Percent Black, non-Hispanicb
|
−0.4 (−1.6, 0.7)
|
0.481
|
−1.1 (−2.4, 0.2)
|
0.101
|
−1.2 (−1.5, −1.0)
|
< 0.0001
|
1.0 (−0.9, 2.9)
|
0.289
|
|
Percent Hispanicb
|
−0.8 (−1.5, 0.0)
|
0.045
|
4.0 (3.1, 5.0)
|
< 0.0001
|
1.9 (1.6, 2.2)
|
< 0.0001
|
1.4 (1.1, 1.7)
|
< 0.0001
|
|
Percent povertyb
|
0.8 (−0.4, 2.0)
|
0.181
|
−3.8 (−5.0, −2.6)
|
< 0.0001
|
−0.6 (−1.2, 0.1)
|
0.116
|
−1.7 (−2.4, −1.0)
|
< 0.0001
|
|
Percent home ownershipb
|
0.4 (−0.4, 1.2)
|
0.331
|
--e
| |
0.5 (0.0, 1.0)
|
0.063
|
−1.3 (−1.9, −0.7)
|
< 0.0001
|
|
Percent urban householdsb
|
−0.4 (−0.6, −0.3)
|
< 0.0001
|
0.2 (0.1, 0.4)
|
0.003
|
0.1 (0.0, 0.2)
|
0.083
|
--e
| |
|
System size: Smallc
|
33.0 (23.2, 43.6)
|
< 0.0001
|
30.4 (18.2, 44.0)
|
< 0.0001
|
−8.9 (−15.0, −2.5)
|
0.011
|
3.5 (−4.5, 12.3)
|
0.402
|
|
System size: Mediumc
|
54.4 (36.6, 74.5)
|
< 0.0001
|
27.3 (9.6, 48.0)
|
0.002
|
−14.8 (−21.8, −7.2)
|
0.0003
|
18.5 (3.9, 35.2)
|
0.012
|
|
System size: Largec
|
103 (74.1, 137)
|
< 0.0001
|
35.9 (13.5, 62.6)
|
0.0008
|
−11.2 (−20.5, −0.9)
|
0.036
|
38.8 (21.0, 59.1)
|
< 0.0001
|
|
System size: V. Largec
|
223 (102, 418)
|
< 0.0001
|
23.1 (−18.5, 85.9)
|
0.324
|
−14.8 (−33.6, 9.3)
|
0.208
|
98.6 (47.3, 168)
|
< 0.0001
|
|
Source water: Groundwaterd
|
−14.8 (−27.3, −0.1)
|
0.049
|
53.3 (34.7, 74.4)
|
< 0.0001
|
−16.6 (−24.3, −8.1)
|
0.0003
|
139 (115, 167)
|
< 0.0001
|
|
Percent croplandb
|
−0.2 (−0.3, 0.0)
|
0.100
|
1.4 (0.8, 2.1)
|
< 0.0001
|
1.4 (1.2, 1.6)
|
< 0.0001
|
0.5 (0.2, 0.7)
|
0.0006
|
|
Livestock per 100 acresb
|
0.1 (−0.1, 0.2)
|
0.304
|
0.7 (0.3, 1.1)
|
0.0005
|
−0.1 (−0.3, 0.0)
|
0.085
|
1.7 (1.2, 2.2)
|
< 0.0001
|
- Note: Percent change in nitrate concentration from pooled regression results using county-level demographic, land use, and water system characteristics in each of the four U.S. regions. Models include state-specific random intercepts and a fixed intercept term
- aFor a visual depiction of which states are in each U.S. region, refer to Fig. 1
- bContinuous predictor, table estimates reflect effect of one-unit change in the predictor
- cReferent group: very small systems. dReferent group: surface water. eNot included in final model
