The last decade has seen a blossoming of research on the long-term effects of early childhood conditions across a range of disciplines. In economics, the focus is on how human capital accumulation responds to the early childhood environment. This work has been spurred by a growing realisation that early life conditions can have persistent and profound impacts on later life. Cunha and Heckman (2008) and Cunha et al. (2010) estimate structural models in which initial endowments and investments feed through to later outcomes. They conclude that measured endowments account for up to 15% of adult educational attainment.
A survey of new work
In Almond and Currie (forthcoming), we survey this growing and dynamic literature. A striking conclusion is that events before birth can be critical determinants of future outcomes. Indeed, this influence can be stronger than that from comparable exposures during subsequent phases of early childhood.
For example, in previous research one of us (Douglas Almond 2006) examines the long-term effects of prenatal exposure to influenza in the 1918 Pandemic. The timing of the epidemic can be precisely tracked by looking at spikes in mortality rates. This research follows cohorts who were affected in utero in the 1960-1980 US Censuses and compares them to cohorts born just earlier (and thereby experiencing the Pandemic in early childhood) or just later. The study finds a large, negative impact across a range of later-life outcomes. For example, it estimates that children of infected mothers were 15% less likely to graduate high school and that their wages were between 5% and 9% lower than the comparison cohorts.
Recently, Kelly (2009) has found negative effects of prenatal exposure to the 1957 “Asian flu” on birth weight and future test scores in Great Britain. Meanwhile Field et al. (2009) find that prenatal iodine supplementation, which was offered episodically in Tanzania, increased educational attainment in Tanzania by half a year, with larger impacts for girls.
Exploiting a natural experiment
In another forthcoming piece of research, Reed Walker has worked with one of us (Currie and Walker forthcoming) to exploit a natural experiment involving the introduction of electronic toll collection devices (E-ZPass) in New Jersey and Pennsylvania. Since much of the pollution produced by automobiles occurs when idling or accelerating back to highway speed, electronic toll collection greatly reduces auto emissions in the vicinity of a toll plaza, they compare mothers near toll plazas to those who live near busy roadways but further from toll plazas. They find that E-ZPass increased birth weight and gestation, outcomes that have been linked to future educational attainments (Black et al. 2007).
Despite this evident, heightened sensitivity of birth and later life outcomes to the prenatal period should not justify fatalism. While children can be permanently damaged in utero, many studies suggest that at least some of the damage can be remediated. The picture that emerges is one of vulnerability but also of resilience. In our forthcoming survey, we focus on three kinds of programmes which have been proven to make a difference in rigorous studies: nurse home visiting programmes, the Supplemental Feeding Program for Women, Infants, and Children, and enhanced preschool programmes such as Perry Preschool, Abcedarian, and Head Start.
David Olds and collaborators have developed a particular model for home visiting and conducted randomised controlled trials in a number of settings to evaluate it (Olds et al, 2007). Olds' programmes focus on families that are at risk because the mother is young, poor, uneducated and/or unmarried, and involve home visits by trained public health nurses from the prenatal period up to two years post-partum. The evaluations have shown many positive effects on maternal behaviour, and on child outcomes.
As of two years of age, children in Elmira, New York were much less likely to have been seen in a hospital emergency room for unintentional injuries or ingestion of poisonous substances, although this finding was not replicated at other study sites. As of age 15, children of visited mothers were less likely to have been arrested or to have run away from home, had fewer sexual partners, and smoked and drank less. The children were also less likely to have been involved in verified incidents of child maltreatment.
In one of the most striking and recent studies to document positive effects of the Supplemental Feeding Program for Women, Infants, and Children, Hoynes et al. (2009) use the initial roll-out of the programme in the 1970s to identify its effects. They find that the implementation of the programme increased average birth weight by 10% and decreased the fraction of low birth weight births. Deming (2009) replicates the results of Currie and Thomas (1995) using the same cohorts of children from the National Longitudinal Surveys, observed at older ages. He finds that Head Start closes about 1/3 of the gap between Head Start and other, less disadvantaged children and notes that projected gains in earnings are enough to offset the cost of the programme.
In summary, the evidence certainly indicates that events while children are in utero are important to their later development. This does not mean that efforts to remediate these impacts are doomed to failure, as successful intervention programmes show. It does however have implications for the timing of social interventions designed to mitigate harms, suggesting that interventions should be targeted at pregnant women and/or women of child bearing age in addition to young children.
Almond, Douglas (2006), “Is the 1918 Influenza Pandemic Over? Long-term Effects of In Utero Influenza Exposure in the Post-1940 U.S. Population”, Journal of Political Economy, 114:672-712.
Almond, Douglas and Janet Currie (forthcoming), "Human Capital Development Before Five", in David Card and Orley Ashenfelter (eds.), Handbook of Labour Economics.
Black, Sandra, Paul Devereux, and Kjell Salvanes (2007), “From the Cradle to the Labour Market? The Effect of Birth Weight on Adult Outcomes”, Quarterly Journal of Economics, 122 (1):409-439.
Cunha, Flavio and James Heckman (2008), “Formulating, Identifying and Estimating the Technology of Cognitive and Noncognitive Skill Formation,” The Journal of Human Resources, XLIII(4):737-782.
Cunha, Falvio, James Heckman, and Susanne Schennach (forthcoming). “Estimating the Technology of Cognitive and Noncognitive Skill Formation”, Econometrica.
Currie, Janet and Duncan Thomas (1995), "Does Head Start Make A Difference?”, The American Economic Review, 85(3):341-364, June.
Currie, Janet and Reed Walker (forthcoming), "Traffic Congestion and Infant Health: Evidence from E-ZPass", American Economic Journals-Applied Economics.
Deming, David (2008), “Early Childhood Intervention and Life-Cycle Skill Development”, Accepted for publication: American Economic Journal: Applied Economics.
Field, Erica, Omar Robles and Maximo Torero (2009), “Iodine Deficiency and School Attainment in Tanzania”, American Economic Journal: Applied Economics, 1(4):140-169, October.
Hilary Hoynes, Marianne E. Page, Ann Huff Stevens (2009), “Is a WIC Start a Better Start? Evaluating WIC’s Impact on Infant Health Using Program Introduction”, NBER Working Paper 15589.
Kelly, Elaine (2009), “The Scourge of Asian Flu: in Utero Exposure to Pandemic Influenza and the Development of a Cohort of British Children”, Institute for Fiscal Studies, Working Paper 09/17, University College London.
Olds, David L et al (2007), “Effects of Nurse Home Visiting on Maternal and Child Functioning: Age-9 Follow-up of a Randomized Trial”, Pediatrics, 120:832-845.