An Econometric Model of Birth Inputs and Outputs for Native Americans

This paper presents a new model of the birth process of Native Americans with seven endogenous variables: four birth inputs 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 NLSY. We find 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 effect 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 effects between the birth inputs and outputs. Moreover, G appears dependent on the exogenous size of the mother. BL is affected by the inputs mainly through WG. BW is affected by the inputs through their effects 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 3.240kg