Michael Kremer will be the new Chief Economist of the World Bank. This is one of the most influential positions in an institution that committed $118 billion to development last year. Probably the largest impact you could ever have? Not if your name is Michael Kremer.
The Bank’s own announcement says his work has “reached hundreds of millions of people”. Below are the public counts of people reached, and the measured impacts, of four initiatives he had a hand in. These numbers are hard to pin down, so the critiques and the revised estimates are collected at the bottom.
What if he had gone into finance?
Economists would say that none of these numbers is his impact. The right comparison is the counterfactual: how many fewer lives would have been saved and improved if Michael Kremer had gone into finance? (This is generally a depressing thought exercise for employees in a competitive position with limited autonomy, because the next best hire would probably have done a similar job.) Similarly, donors were going to spend the money on something; what he changed is that it went to programmes with evidence of impact. We don’t know if the evidence drew in more donor money. I order the initiatives by how confident I am in the attribution.
1. The advance market commitment: 215 million children
What is it? Drug companies under-invest in vaccines for diseases of poor countries, because the customers cannot pay enough to cover the research. In a series of papers and a book in the early 2000s, Kremer and co-authors proposed a fix: donors promise in advance to subsidise a vaccine if someone develops it and poor countries want it. In 2007, six donors pledged $1.5 billion to try this for pneumococcus, a bacterium that was killing about half a million children a year.
The impact. Three vaccines were eventually supplied through it. Gavi estimates that they reached more than 215 million children in 60 countries and averted 700,000 deaths by 2020. Similar commitments were used to speed up vaccine supply during the Covid-19 pandemic, and are being proposed in many other contexts, such as carbon capture.
His contribution. The idea, the theory behind the design, and years of selling it, in outlets from economics journals to the New York Times.
Who else? Rachel Glennerster co-wrote the book, Strong Medicine. Jonathan Levin and Christopher Snyder worked out the design. Ruth Levine, Alice Albright and Owen Barder ran the Center for Global Development working group that turned an idea into a proposal. Italy’s finance minister, Giulio Tremonti, carried it through the G7. Italy, the UK, Canada, Russia, Norway and the Gates Foundation paid. Gavi ran it, the World Bank held the money, the WHO certified the vaccines, and UNICEF bought the doses: 161 million of them in 2019 alone.
2. Deworming: two billion treatments
What is it? In the late 1990s Kremer and Edward Miguel worked with a small NGO in western Kenya to phase in deworming pills across 75 schools in random order. Absenteeism fell by a quarter, including among children who never took a pill, because fewer worms were going around. Twenty years later, in this one group of Kenyan children, those who got two to three extra years of deworming consumed 14% more and earned 13% more per hour.
The impact. Kremer then co-founded Deworm the World, now part of Evidence Action, which has helped governments deliver more than two billion treatments since 2014, at under 50 cents each.
His contribution. He ran the study and tirelessly promoted the initiative, then helped to start the organisation that took it to scale.
Who else? Edward Miguel. Paul Lipeyah, a friend working at the NGO, whose conversations with Kremer led to the first randomised evaluation. Sarah Baird, Joan Hamory Hicks, Michael Walker and Owen Ozier, who tracked down 84% of the children twenty years on. Esther Duflo, co-founder of Deworm the World. The governments of Bihar, India and Kenya, which run the programmes. GSK and Johnson & Johnson, which donate the pills. And the staff who hand them out.
3. Safe water: 4 to 9 million reached
What is it? Diarrhoea kills about 440,000 children under five every year, and at least 1.7 billion people drink water contaminated with faeces. Kremer and colleagues tested cheap ways to clean drinking water in Kenya, which grew into Dispensers for Safe Water: chlorine dispensers placed next to village water points. Then he and four co-authors pooled 18 randomised trials and found that treating water cuts deaths among children under five by about a quarter.
The impact. How many people is a matter of what you count. Evidence Action reports that its dispensers and in-line chlorination systems give nearly 10 million people in Kenya, Uganda, Malawi and India access to treated water, and its own model puts the toll at more than 15,000 child deaths averted since 2013. GiveWell, which paid for more than four-fifths of the dispensers from 2022, counts people who actually drink treated water and puts that at 3.7 million a year. The gap between the two, and a further cut in 2026, are explained at the bottom of this post.
His contribution. He produced the evidence.
Who else? Edward Miguel, Jessica Leino, Alix Zwane, Clair Null, Sendhil Mullainathan and Amrita Ahuja on the Kenyan studies. Stephen Luby, Ricardo Maertens, Brandon Tan and Witold Więcek on the mortality paper. Innovations for Poverty Action and Evidence Action built and ran the programme, and GiveWell’s donors and Open Philanthropy paid for more than four-fifths of it from 2022.
4. A venture fund inside USAID: 200 million people
What is it? In 2010 Kremer and Maura O’Neill set up Development Innovation Ventures inside USAID. It made small grants to test innovative ideas and bigger grants to scale successful ones. Venture capital for development.
The impact. Kremer and co-authors went back to the first three years of grants. The fund had spent $19 million on 41 ideas, or $16 million once discounted. By his own team’s deliberately conservative estimate, five of those ideas alone produced $281 million in benefits, or $17 for every discounted dollar spent on the whole portfolio, even if the other 36 achieved nothing. The World Bank says the fund went on to back more than 300 innovations reaching more than 200 million people.
His contribution. He designed the fund and was its scientific director for fifteen years. He invented none of the things it funded.
Who else? Maura O’Neill. The staff of the fund, among them Sasha Gallant and Jeff Brown, who relaunched it as a non-profit this year after USAID was shut down. Researchers who ran the different studies. The people who built software for community health workers, sold affordable reading glasses, and put stickers in Kenyan minibuses telling passengers to shout at reckless drivers. And the US taxpayer, until recently.
Table 1. The scorecard
| People reached | What the studies found | Revised GiveWell estimates | Total impact (and who counted) | |
|---|---|---|---|---|
| Advance market commitment | 215m children vaccinated (Gavi) | — | — | 700,000 deaths averted by 2020 (Gavi’s model) |
| Deworming | 2bn treatments since 2014; 280m children in 2019 (Evidence Action) | +14% consumption 20 years on, in one Kenyan cohort | about 13% of that effect, for today’s lower worm loads | not computed |
| Safe water | ~9m living near a dispenser (Evidence Action); 3.7m a year drinking treated water (GiveWell) | −25% deaths among under-fives, across 18 trials | −12% | ~15,000 under-five deaths averted (Evidence Action); 7,600 deaths averted (GiveWell) |
| USAID innovation fund | 200m+ people; 99m from the first three years (World Bank; Kremer’s team) | — | — | $281m of benefits from five of 41 ideas, $17 per $1 (Kremer’s team; “not a causal estimate”) |
The rows slightly overlap: the chlorine dispensers appear in both the water and the innovation-fund rows, and the same child can be vaccinated and dewormed.
Beyond the four
Beyond the directly attributable impacts above, he also had an indirect impact through his teaching, supervision, guidance, and contributions to the RCT movement in development economics. He supervised rock-stars in international development who themselves have done great things. Examples include Edward Miguel, Benjamin Olken, Karthik Muralidharan, Seema Jayachandran, Pascaline Dupas, Nava Ashraf, James Habyarimana and David Evans. Alix Zwane, a co-author from one of the water studies, became the first director of Evidence Action, the organisation that now runs both the deworming and the chlorine programmes. I cannot put a number on any of this.
What does this mean for you?
If you are anything like me, you can only dream of such an impact. I will claim professional success with a fraction of one of these initiatives. Nonetheless, four things stand out.
Big wins remain in international development. Wherever there are market failures, government failures, or poverty traps, a targeted intervention can have an outsized impact. GiveWell expects to allocate a billion dollars to programmes it estimates do at least 8 times as much good per dollar as giving cash to the poor. In water alone it found $125 million worth.
Your contribution is needed. None of these would have worked on one person’s effort alone. A vaccine subsidy needs someone to negotiate the contract. A deworming day needs a teacher with a box of pills and a class register. The first experiment needed Paul Lipeyah.
Seek unique experiences and time in the field. After his undergraduate degree, Kremer travelled to Kenya intending to visit for a few weeks, and stayed for a year. This inspired him to run some of the first randomised controlled trials in development economics, which kicked off the RCT revolution. As AI becomes an equaliser in technical skills, I believe that a unique background will become more valuable than ever. Visiting schools and talking to teachers and head teachers has deepened my understanding and made me a better researcher.
Small things count. A kind word to someone in need; stepping in at a moment of cruelty; treating others with dignity. I admit this does not follow from a table of impact estimates. But David Evans, a former student, writes that Kremer is, in Pamela Jakiela’s words, “one of the kindest and most constructive” economists working today, and that this is part of why his work travels. You will never know the lasting impact a small kindness has on someone’s life.
Which brings me back to the new job. Chief Economist is the item on this list where he is most replaceable. It may still turn out to be the biggest.
Who’s counting?
Impact is hard to measure, especially once a programme scales into new contexts, and the reach figures above mostly come from the organisations that ran the programmes. People make mistakes. So most of these numbers have been debated, which is a good thing. The initiatives nonetheless scaled interventions with credible evidence behind them, which is more than can be said for most of what donors fund.
The vaccines. The 700,000 comes from a model, not a count. Médecins Sans Frontières points out that 82% of the money went to Pfizer and GSK, that a pneumococcal vaccine had been on the market since 2000, and that prices fell by only about 15%. Kremer, Levin and Snyder’s own assessment puts the cost at $83 per year of healthy life bought, which is cheap by any standard.
Deworming. The income gains come from one group of Kenyan children who had far more worms than children in today’s programmes. GiveWell, which funds deworming, keeps only about 13% of the measured effect in its own calculations. Even so, it estimates that its deworming grants in India did about 8 times as much good per dollar as handing out cash. And let’s not get into the messy worm wars.
Safe water. Two revisions. First, a quarter of all deaths among under-fives is more than diarrhoea alone would explain, so GiveWell uses about 12% in its own calculations. On that basis it puts the deaths averted by its $65 million grant, which covered more than four-fifths of the dispenser budget from 2022, at about 7,600, and its count of people actually drinking treated water at 3.7 million a year, against the 9 million or so Evidence Action counts as living near a dispenser. Second, in March 2026 Evidence Action reported that independent surveys by Kremer’s own lab had found 70% fewer people with detectable chlorine in their water than Evidence Action’s monitoring showed. It has closed the programme in Malawi and halved it in Uganda; what remains serves about 2.8 million people. Its 15,000 deaths averted rest on the monitoring that overstated use, so the true figure is lower, though nobody has said by how much. To its credit, it published the finding itself.
The innovation fund. The $17 is the estimate of Kremer’s own team, and the paper says in as many words that it “does not yield a causal estimate”. One of the five ideas that produced the measured benefits was the chlorine dispensers of the previous row, so the two rows are partly the same success counted twice.
Acknowledgements. The blog would not exist without Claude Code, who tracked down and verified the numbers, or David Evans, who wrote an excellent piece on Kremer’s contribution. No lives were saved during the writing of this blog.