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This paper presents a new model of the birth process of Native Americans with seven endogenous variables: four birthinputs maternal smoking (S), drinking (D), prenatal care (PC), and weight gain (WG), and three birth outputs gestational age (G), birth length (BL), and birth weight (BW). The model is a seven-equation simultaneous model with three endogenous dummies S, D, and PC. The data are taken from the National Longitudinal Survey of Youth (NLSY). We 5nd that the four birth inputs are determined jointly and dependently among S, D, and PC, but independently of WG. S has negative systematic correlation with G. D and PC appear to have no sizeable systematic e8ect on G, BL, or BW. Except for the sizeable and positive correlation between the unexplained parts of S and G, there seem to be no unexplained common e8ects between the birth inputs and outputs. Moreover, G appears dependent on the exogenous size of the mother. BL is a8ected by the inputs mainly through WG. BW is a8ected by the inputs through their e8ects on G. Except for maternal weight, there is little correlation between the remaining exogenous variables and BW. Finally, the predictive density of BW for a typical pregnancy gives a mean weight of 3:240 kg. c 2002 Elsevier Science B.V. All rights reserved. |
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