Health in Utero, Parental Investment, and Human Capital Development

Using administrative data on Colorado birth certificates matched to schooling outcomes, we investigate the relationship between birth weight, birth spacing, and educational attainment.  As far as we know this is the first study to do this using matched large scale birth and elementary to high school administrative data.

To mitigate endogeneity, we use mother fixed effects for twins (as in Figlio et al. 2014) and singleton sibling births.  We also use a miscarriage as an instrument for birth spacing (as in Buckles and Munnich 2012).  For twins, we find a strong positive effect of birth weight on math scores, with a smaller in magnitude but still positive effect for readings scores. Following Figlio et al., we average math and reading scores and find that a 10 percent increase in birth weight results in a 0.03 SD increase in test scores for grades 3-8. These effects dissipate slightly for 9-10^th grade scores to 0.02 SD.  Siblings who are singletons shows a similarly persistent, though smaller, effect of birth weight on math and reading for 3-8^th grades. A 10 percent increase in birth weight results in a 0.02 SD increase in average math and reading scores. These results shrink in half for grades 9 and 10, however, most of this dissipating effect occurs for reading scores, while the effect of birth weight on math scores remains persistent through high school.

With regard to birth spacing, miscarriage is a strongly relevant instrument for birth spacing, increasing the spacing by 1.18 years (F stat = 637). Miscarriage also decreases the likelihood of having a gap between children of shorter than 2 years by 23 percentage points (F stat= 511).  We find that a larger space between siblings results in a significant negative effect for the first (oldest) child’s reading, writing, and math scores pooled for grades 3-10. For example, for math, a one-year increase in spacing decreases test scores by 0.05 SD. Similarly, there is a positive effect of spacing of shorter than 2 years on three subject scores. For the second (youngest) child, we find a statistically significant positive effect of a larger space between siblings for reading, writing and math scores and a gap of less than 2 years results in a reduction in these scores. A one-year increase in birth spacing increases math and reading scores by 0.03 SD and 0.04 SD, respectively. Focusing, however, only grades 9 and 10, we find statistically insignificant results for the older child and only marginal statistically significant positive effects of birth spacing for the younger child.  This suggests that the effects of birth spacing dissipate as the children get older.

Finally, using miscarriage as an instrument, we find a negative effect of birth spacing on the birth weight of the second child, reducing average birth weight by 18 grams or a little less than 1% from the mean (mean=3275 grams). To our knowledge this study is the first to investigate the link between birth spacing and birth weight using miscarriage as an instrument.