Table 1.
Study population characteristics for unexposed and exposed subjects from rural Colorado 1996–2009.
| Maternal or infant characteristic | Total | Referent group (0 wells within 10 miles) | Low (first tertile)a | Medium (second tertile)a | High (third tertile)a |
|---|---|---|---|---|---|
| Total n (%) | 124,842 | 66,626 (53) | 19,214 (15) | 19,209 (15) | 19,793 (16) |
| Median | 27 | 27 | 26 | 27 | 27 |
| 25th percentile | 22 | 22 | 21 | 22 | 23 |
| 75th percentile | 32 | 32 | 30 | 31 | 31 |
| Maternal ethnicity (%)b | |||||
| Non-Hispanic white | 73 | 74 | 72 | 76 | 69 |
| Sex (%) | |||||
| Male | 51 | 51 | 51 | 51 | 51 |
| Maternal smoking (%)c | |||||
| Smokers | 11 | 11 | 14 | 13 | 8 |
| Maternal alcohol (%)c | |||||
| No | 99 | 98 | 99 | 99 | 99 |
| Parity (%) | |||||
| 0 | 33 | 33 | 31 | 32 | 32 |
| 1 | 23 | 23 | 24 | 24 | 25 |
| 2 | 19 | 19 | 20 | 19 | 20 |
| > 2 | 25 | 25 | 26 | 25 | 24 |
| Residential elevation (feet) | |||||
| Median | 5,000–5,999 | 6,000–6,999 | < 5,000 | 5,000–5,999 | < 5,000 |
| 25th percentile | < 5,000 | 5,000–5,999 | < 5,000 | < 5,000 | < 5,000 |
| 75th percentile | 7,000–7,999 | 7,000–7,999 | 5,000–5,999 | 6,000–6,999 | 5,000–5,999 |
| Maternal education (%) | |||||
| < 12 years | 21 | 20 | 26 | 19 | 22 |
| 12 years | 30 | 30 | 33 | 29 | 28 |
| 13–15 years | 23 | 22 | 25 | 25 | 24 |
| ≥ 16 years | 26 | 28 | 18 | 26 | 27 |
| aFirst tertile, 1–3.62 wells/mile; second tertile, 3.63–125 wells/mile; third tertile, 126–1,400 wells/mile. bIncludes both Non-Hispanic and Hispanic white. cDuring pregnancy. | |||||