Global Health Economics
Deworming and the Search for Cost-Effective Aid
How a famous study of school deworming in Kenya shaped ideas about cost-effective health interventions, and why its findings sparked a lively debate.
Can a pill costing a few cents improve children’s education and future earnings? A famous study suggested yes, and sparked one of global health’s most interesting debates.
The Kenya study
In 1998, economists Edward Miguel and Michael Kremer evaluated a programme that provided deworming pills to children in schools in western Kenya. Schools were phased in randomly, allowing comparison.
Their 2004 paper found:
- School absence fell substantially in treated schools.
- Benefits spilled over to untreated children nearby, because fewer worms spread in the community.
- Treatment cost very little per child.
Long-term effects
Follow-up studies tracking the same children for decades found that those who received more years of deworming had higher earnings and consumption as adults.
The “worm wars”
In 2015, a team of researchers re-analysed the original data and found some errors, and questioned some results. Other reviews, notably by the Cochrane Collaboration, found little evidence that mass deworming improves child health or school outcomes on average.
Supporters argued the long-term economic benefits were substantial and that the core findings held up. The debate, nicknamed the “worm wars”, showed how evidence is tested and challenged in public.
Why it matters
- It highlighted the value of randomised evaluations in development.
- It showed the importance of replication and transparency.
- It raised questions about acting on uncertain but potentially large benefits at low cost.
Charity evaluator GiveWell continues to recommend some deworming charities, reasoning that even if the probability of large benefits is uncertain, the low cost makes the expected value high.
India’s programme
India runs National Deworming Day twice a year, giving deworming tablets to children and adolescents through schools and anganwadis.
Kremer’s Nobel
Michael Kremer shared the 2019 Nobel prize in economics with Abhijit Banerjee and Esther Duflo for their experimental approach to alleviating global poverty.
A health minister must decide whether to fund deworming for all schoolchildren. Evidence of short-term health benefits is mixed, but some studies suggest large long-term gains, and the cost per child is tiny. She decides the potential benefits justify the small cost, while funding further research.
Important findings need replication and scrutiny. The deworming debate shows how evidence evolves.
- Miguel and Kremer found school deworming in Kenya reduced absence at very low cost.
- Long-term follow-ups found higher adult earnings.
- Re-analyses and reviews questioned the average effects, sparking the worm wars.
- The debate highlighted randomised trials, replication and cost-effectiveness.
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