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Table 5 Regression results for nitrate in community water systems stratified by region

From: Environmental justice and drinking water quality: are there socioeconomic disparities in nitrate levels in U.S. drinking water?

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
  1. 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
  2. aFor a visual depiction of which states are in each U.S. region, refer to Fig. 1
  3. bContinuous predictor, table estimates reflect effect of one-unit change in the predictor
  4. cReferent group: very small systems. dReferent group: surface water. eNot included in final model