Exploiting Externalities to Estimate the Long-Term Effects of Early Childhood Deworming

This paper investigates whether a large-scale deworming intervention aimed at primary school pupils in western Kenya had long-term effects on young children in the region. The paper exploits positive externalities from the program to estimate the impact on younger children who did not receive treatment directly.In 2009 and 2010, a field team in Kenya collected height, weight, and migration data from more than 20,000 children at all of the deworming project schools in Samia and Bunyala districts of Kenya's Western Province. For a subset of just over 2,400 children, the team also conducted detailed cognitive assessments. Children from the same age cohorts were included during both data collection years: in 2009, this meant including every child between the ages of 8 and 14; in 2010, it meant every child between the ages of 9 and 15.

Ten years after the intervention, large cognitive effects are found—comparable to between 0.5 and 0.8 years of schooling—for children who were less than one year old when their communities received mass deworming treatment. Because mass deworming was administered through schools, effects are estimated among children who were likely to have older siblings in schools receiving the treatment directly; in this subpopulation, effects are nearly twice as large. I find large effects on cognitive performance equivalent to half a year of schooling, robust to a variety of specifications, more than ten years after the original intervention. Effects are strongest among those who were likely to have an older sibling in school at the time of the original intervention—and particularly so if that sibling was female—as one might expect from an epidemiological perspective.