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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

From: Area-level risk factors for adverse birth outcomes: trends in urban and rural settings

 

Population density

 

1sttertile

2ndtertile

3rdtertile

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)

  1. 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.
  2. Model 2 includes model 1 variables adding parity, payment method, education, race, and a natural spline for mother’s age.