The effects of demographics and maternal behavior on the distribution of birth outcomes
This paper utilizes quantile-regression techniques in order to estimate the effects of demographics and maternal behavior during pregnancy at various quantiles of the birthweight distribution. Due to the high costs and longterm effects (both medical and e
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Abstract. This paper utilizes quantile-regression techniques in order to estimate the effects of demographics and maternal behavior during pregnancy at various quantiles of the birthweight distribution. Due to the high costs and longterm effects (both medical and economic) associated with low-birthweight babies, there is a great deal of interest in quantifying these effects, particularly at the lower end of the birthweight distribution. Using large samples of 1992 and 1996 births in the United States, the quantile-regression estimates indicate that several factors (including race, education, and prenatal care) have a significantly higher impact at lower quantiles and lower impact at higher quantiles. These effects at lower quantiles are underestimated by least-squares regression estimates. The inequality in birthweights implied by these results is quite significant, and there is little indication that the inequality has changed much in recent years. Key words: birthweight, natality, quantile regression JEL classification: e2I, I I 0 1. Introduction
The birthweight of children has long been a concern of the public-health community. Births of low-birthweight babies, generally defined as those
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Financial support from the University of Chicago Graduate School of Business is gratefully acknowledged. This paper has benefited from the comments of Bernd Fitzenberger' and two anonymous referees. I am indebted to Roger Koenker and Kevin Hallock, who pointed out an error in my original data. B. Fitzenberger et al. (eds.), Economic Applications of Quantile Regression © Springer-Verlag Berlin Heidelberg 2002
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weighing less than 2500 grams (around 5.5 pounds), result in both economic costs for society and for the children themselves. First, the direct costs for newborn care are extremely high for lowbirthweight babies. For instance, in the United States, Lewit et. al. (1995) estimate that 35% of health-care costs during the first year of life are spent on low-birthweight babies, which account for less than 10% of total births. Joyce (1999) estimates that the marginal cost (in terms of newborn care before release from the hospital) of birthweight is approximately $6-10 per gram, with higher marginal costs at lower birthweights. Low-birthweight babies also have a much higher incidence of infant mortality. Disorders related to short gestation and low birthweight are the leading cause of infant mortality among black babies and the third leading cause of infant mortality among white babies. 1 Second, there is evidence that the effects of low birthweight are long-term. Hack et. al. (1995), for example, discuss the developmental problems most prevalent among low-birthweight infants. Corman (1995) finds that children who were low birthweight are not as healthy as other children and are more likely to delay entry into kindergarten. Corman and Chaikind (1998) find that low-birthweight children are more likely to repeat a grade in school and attend special-education classes.
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