Table 2.
The Zero-Inflated Poisson Model for Generalized Propensity Score
| A. Poisson Model for Months Breast-feeding Duration | B. Logit Model for Latent Class, “No Breastfeeding” | Marginal Effects | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Covariates | Factor Change† | 95% CI | Odds Ratio | 95% CI | ME | 95% CI | |||
| Child (at 1997 survey) | |||||||||
| Female | 1.060* | 1.004 | 1.118 | 1.015 | 0.819 | 1.257 | 0.139 | −0.206 | 0.480 |
| Age (years) | 1.003 | 0.994 | 1.012 | 1.004** | 1.001 | 1.007 | −0.006* | −0.010 | 0.000 |
| No. of siblings | 0.966* | 0.940 | 0.992 | 0.849** | 0.761 | 0.948 | 0.142 | −0.034 | 0.320 |
| First born | 0.983 | 0.922 | 1.048 | 0.684** | 0.524 | 0.892 | 0.505* | 0.081 | 0.930 |
| Black | 0.950 | 0.873 | 1.035 | 2.882*** | 2.179 | 3.810 | −1.620*** | −2.039 | −1.200 |
| HOME measure‡ | 0.996 | 0.985 | 1.007 | 0.976 | 0.932 | 1.021 | 0.025 | −0.047 | 0.100 |
| Born preterm | 0.878 | 0.769 | 1.002 | 1.282 | 0.839 | 1.959 | −0.662* | −1.271 | −0.050 |
| Born small for gestational age | 1.046 | 0.946 | 1.157 | 1.380 | 0.984 | 1.937 | −0.353 | −0.906 | 0.200 |
| Child's health status at birth§ | 1.042 | 0.994 | 1.092 | 0.688*** | 0.567 | 0.833 | 0.660*** | 0.352 | 0.970 |
| Mother (at 1997 survey) | |||||||||
| WIC participation | 0.998 | 0.908 | 1.097 | 1.387* | 1.020 | 1.886 | −0.480 | −0.984 | 0.020 |
| Mom's age giving birth (years) − 20 | 1.015*** | 1.009 | 1.022 | 0.967* | 0.943 | 0.993 | 0.090*** | 0.048 | 0.130 |
| IQ | 1.014*** | 1.006 | 1.021 | 0.922*** | 0.897 | 0.947 | 0.157*** | 0.113 | 0.200 |
| Education | |||||||||
| High school graduate | 0.780*** | 0.691 | 0.879 | 0.964 | 0.660 | 1.407 | −0.617* | −1.228 | −0.010 |
| College or more | 0.874* | 0.769 | 0.994 | 0.599* | 0.393 | 0.911 | 0.372 | −0.323 | 1.070 |
| Mother (year of child birth) | |||||||||
| Annual family income ($) | 0.951* | 0.907 | 0.997 | 1.014 | 0.847 | 1.215 | −0.160 | −0.452 | 0.130 |
| Married | 0.940 | 0.837 | 1.056 | 0.787 | 0.544 | 1.140 | 0.183 | −0.443 | 0.810 |
| Employed | 0.835*** | 0.788 | 0.885 | 1.115 | 0.882 | 1.411 | −0.655*** | −1.033 | −0.280 |
| Head of household¶ | 0.813** | 0.702 | 0.941 | 1.093 | 0.706 | 1.693 | −0.646* | −1.291 | 0.000 |
| Self-rated health status‖ | 1.026 | 0.992 | 1.060 | 0.965 | 0.852 | 1.093 | 0.122 | −0.081 | 0.320 |
| Received Medicaid during pregnancy | 0.922 | 0.832 | 1.022 | 0.821 | 0.580 | 1.162 | 0.059 | −0.506 | 0.620 |
| Constant | 5.134*** | 3.543 | 7.439 | 60.076*** | 14.627 | 246.738 | |||
*Significant at .05 level; **significant at .01 level; ***significant at .001 level.
†
Change in the expected months of breast-feeding resulted from one unit of change in the covariate, holding other covariates constant.
‡
Home observation for measurement of the environment scale.
§
1: Worse; 2: Same; 3: Better (as compared with other babies born at birth).
¶
Indicates that mother was the only adult in the household.
‖
1: Poor; 2: Fair; 3: Good; 4: Very good; 5: Excellent.