TY  - JOUR
AU  - Conley,Dalton
AU  - Strully,Kate
AU  - Bennett,Neil G.
TI  - A Pound of Flesh or Just Proxy? Using Twin Differences to Estimate the Effect of Birth Weight on Life Chances
JF  - National Bureau of Economic Research Working Paper Series
VL  - No. 9901
PY  - 2003
Y2  - August 2003
UR  - http://www.nber.org/papers/w9901
L1  - http://www.nber.org/papers/w9901.pdf
N1  - Author contact info:
Dalton Conley
New York University
249 West 29th Street #2E
New York, NY  10001-5230
Tel: 212/998-7580
Fax: 212/995-4140
E-Mail: conley@nyu.edu

Kate Strully
E-Mail: kstrully@albany.edu

Neil G. Bennett
Baruch College/
CUNY Institute for Demographic Research
Box D-901
One Bernard Baruch Way
New York, NY  10010
Tel: 646/660-6779
Fax: 646/660-6784
E-Mail: Neil.Bennett@baruch.cuny.edu
AB  - Recent research into the implications of low birth weight may be plagued by unobserved variable bias. It is unclear whether the later-life consequences found to be associated with low birth weight are a true effect of  poundage' at birth, or whether this association results from underlying factors related to birth weight   such as genetics, gestational age, pregnancy-related behavior, or prenatal environment. In this study, we employ twin comparisons to rule out such unobserved factors and to isolate more precise effects of birth weight on infant mortality. Using data from the 1995-1997 Matched Multiple Birth Database and deducing zygosity based on the sex ratio of twin births, we examine the effects of birth weight for both fraternal and identical twins on both neonatal and post-neonatal mortality. Results suggest that in the neonatal period, low birth weight may partially be acting as a proxy for underlying genetic conditions, but in the post-neonatal period birth weight per se increases the risk of mortality. Thus, it appears that after an initial weeding-out' period in which the more severe ailments associated with genetics may be behind birth weight effects,  poundage' itself has a significant impact on life chances net of genes and other pregnancy-specific health or social conditions.
ER  -