Table 3

Multilevel logistic regression analysis results of preterm birth risk by quartile of county-level poverty, entire study population

PTB (< 35 wk)
 PTB (< 32 wk)


OR (95% CI)
 IOR-80 *
 MOR†
 OR (95% CI)
 IOR-80 *
 MOR†
Model I: Poverty Only
 1.21

1.22
     2nd Quartile
 1.14 (0.94, 1.38)
 0.79, 1.63
1.15 (0.92, 1.43)
 0.79, 1.68
3rd Quartile
 1.28(1.06, 1.55)
 0.89, 1.83
1.33 (1.07, 1.65)
 0.91, 1.94
4th Quartile
 1.30(1.09, 1.56)
 0.91, 1.87
1.40 (1.14, 1.72)
 0.96, 2.05







Model II: Model I + Demographic factors
 1.10

1.07
2nd Quartile
 1.09 (0.97, 1.22)
 0.91, 1.31
1.09 (0.97, 1.23)
 0.96, 1.24
3rd Quartile
 1.18 (1.06, 1.32)
 0.99, 1.42
1.24 (1.10, 1.39)
 1.09, 1.41
4th Quartile
 1.15 (1.04, 1.28)
 0.96, 1.39
1.25 (1.12, 1.41)
 1.10, 1.43







Model III: Model II + Prenatal Care
 1.11

1.09
2nd Quartile
 1.09 (0.97, 1.22)
 0.90, 1.32
1.09 (0.96, 1.25)
 0.92, 1.30
3rd Quartile
 1.19 (1.06, 1.33)
 0.98, 1.44
1.23 (1.08, 1.40)
 1.04, 1.46
4th Quartile
 1.15 (1.03, 1.28)
 0.95, 1.39
1.23 (1.08, 1.39)
 1.03, 1.46







Model IV: Model III + Behaviors
 1.11

1.10
2nd Quartile
 1.09 (0.97, 1.23)
 0.90, 1.33
1.10 (0.96, 1.25)
 0.92, 1.31
3rd Quartile
 1.19 (1.06, 1.34)
 0.99, 1.45
1.24 (1.08, 1.41)
 1.04, 1.47
4th Quartile
 1.16 (1.04, 1.30)
 0.96, 1.41
1.24 (1.09, 1.41)
 1.04, 1.48







Model V: Model III + Medical Risk Factors
 1.14

1.18
2nd Quartile
 1.12 (0.97, 1.29)
 0.87, 1.44
1.13 (0.94, 1.37)
 0.83, 1.55
3rd Quartile
 1.23 (1.07, 1.42)
 0.95, 1.59
1.28 (1.06, 1.55)
 0.94, 1.75
4th Quartile
 1.18 (1.03, 1.35)
 0.91, 1.52
1.27 (1.06, 1.52)
 0.93, 1.73

Refer to table 1 for a complete list of co-variates included in each model

*IOR-80 = 80% interval odds ratio

†MOR = median odds ratio

DeFranco et al. BMC Public Health 2008 8:316   doi:10.1186/1471-2458-8-316