Table 2.
Odds ratios for associations between ZIP code-level percent poverty or African American with 1991–2010 Alabama preterm birth by population density tertile
| |
Population density |
||
|---|---|---|---|
| 1st tertile | 2nd tertile | 3rd tertile | |
| Model 1: Poverty*population density (interaction P-value = 0.0043) | |||
| 1st quartile |
1.00 |
1.00 |
1.00 |
| 2nd quartile |
1.09 (0.99, 1.20) |
1.00 (0.92, 1.09) |
1.18 (1.04, 1.35) |
| 3rd quartile |
1.12 (1.02, 1.23) |
1.05 (0.95, 1.16) |
1.30 (1.13, 1.49) |
| 4th quartile |
1.22 (1.11, 1.34) |
1.08 (0.95, 1.23) |
1.48 (1.34, 1.64) |
| Model 2: Poverty*population density (interaction P-value = 0.0015) | |||
| 1st quartile |
1.00 |
1.00 |
1.00 |
| 2nd quartile |
1.09 (1.00, 1.18) |
0.96 (0.89, 1.03) |
1.07 (0.96, 1.20) |
| 3rd quartile |
1.06 (0.98, 1.15) |
0.96 (0.88, 1.04) |
1.08 (0.97, 1.22) |
| 4th quartile |
0.99 (0.91, 1.08) |
0.88 (0.78, 0.98) |
1.14 (1.04, 1.24) |
| Model 1: African American*population density (P-value = 0.0084) | |||
| 1st quartile |
1.00 |
1.00 |
1.00 |
| 2nd quartile |
1.06 (0.99, 1.13) |
0.98 (0.91, 1.06) |
0.99 (0.83, 1.19) |
| 3rd quartile |
1.15 (1.07, 1.23) |
1.08 (0.99, 1.18) |
1.22 (1.03, 1.45) |
| 4th quartile |
1.27 (1.19, 1.36) |
1.35 (1.18, 1.56) |
1.54 (1.31, 1.81) |
| Model 2: African American*population density (P-value = 0.071) | |||
| 1st quartile |
1.00 |
1.00 |
1.00 |
| 2nd quartile |
1.00 (0.95, 1.07) |
0.94 (0.88, 1.01) |
0.96 (0.81, 1.13) |
| 3rd quartile |
1.00 (0.94, 1.07) |
0.96 (0.89, 1.05) |
1.06 (0.91, 1.24) |
| 4th quartile | 0.96 (0.90, 1.03) | 1.02 (0.90, 1.17) | 1.11 (0.96, 1.29) |
Model 1 includes ZIP code-level poverty or African American, population density tertile, and interaction term for the ZIP-level variable and population density tertile, adjusted for year with a B-spline.
Model 2 includes model 1 variables adding parity, payment method, education, race, and a natural spline for mother’s age.