VoxDev Development Economics

Nearly every child in a low- or middle-income country now goes to school, but about 70% of 10-year-olds still cannot read or understand a simple text. Researchers have tested ways to fix the problem, and governments want them to work. So why has the needle not moved?
Noam Angrist (Oxford) and nine co-authors argue that the missing piece is the study of implementation itself. In this week's VoxDev Talk, Tim Phillips asks Noam about their framework, just published in Science, that sets out how small tightly controlled experiments can scale to large real-world trials, then into government policy and finally into classrooms. 
As Noam describes, it's not easy to convert good intentions and a clear need to real change. Listen to this week's episode to find out why.
The research behind this episode:
Angrist, Noam, Tahir Andrabi, Stefan Dercon, Sharnic Djaker, James Habyarimana, Michelle Kaffenberger, Clare Leaver, Akshay Mangla, Nompumelelo Mohohlwane, and Abhijeet Singh. 2026. "An Agenda for Implementation Science in Education." Science 393 (6816): 1084-87.
To cite this episode:
Phillips, Tim, and Noam Angrist. 2026. "Implementation science in education: Scaling what works." VoxDev Talks (podcast). 

About the guest

Noam Angrist is Academic Director of the What Works Hub for Global Education and a Senior Research Fellow at the Blavatnik School of Government, University of Oxford. He co-founded Youth Impact, an NGO headquartered in Botswana that scales and tests health and education programmes. His research spans the scale-up and implementation of education programmes, global learning data, and A/B testing in the social sector. He led key parts of the education pillar of the World Bank Human Capital Index.
Research cited in this episode

Learning poverty. A World Bank measure: the share of children who cannot read and understand a simple text by age 10. A 2022 report by the World Bank, UNESCO, UNICEF, FCDO, USAID and the Gates Foundation estimated it at about 70% in low- and middle-income countries, up from 57% before the pandemic. It is the gap between schooling and learning in a single number.
Structured pedagogy and teaching at the right level. Two of the approaches with the strongest evidence for improving learning cheaply. Structured pedagogy gives teachers detailed lesson plans, materials and coaching. Teaching at the right level groups children by what they can do, not by their age or grade. The Global Education Evidence Advisory Panel reviews this evidence for cost-effectiveness; Angrist led the research behind its first report.
The economist as plumber. Esther Duflo's 2017 Richard T. Ely Lecture to the American Economic Association. She argued that economists who help governments design policy must work on the details of implementation, tinkering and adjusting as plumbers do. Duflo, Esther. 2017. "The Economist as Plumber." American Economic Review 107 (5): 1-26.
The voltage effect. John List's term for the drop in impact when a programme that worked in a pilot is expanded. List, John A. 2022. The Voltage Effect: How to Make Good Ideas Great and Great Ideas Scale. New York: Currency.
The What Works Hub for Global Education. A research centre based at the Blavatnik School of Government, funded initially by the UK Foreign, Commonwealth and Development Office and the Gates Foundation. It studies how proven education programmes can be implemented and sustained at scale. More at wwhge.org.
Efficacy and effectiveness trials. Terms borrowed from health research. An efficacy trial asks whether something can work under controlled conditions. An effectiveness trial asks whether it works in the real world: at scale, delivered by government, at a cost governments can pay, and for different groups of children. Most education evidence today comes from efficacy trials.
Adaptive trials and A/B testing. Instead of one large, static experiment, researchers run many small randomised tests, change the programme between rounds, and test again. Angrist's shorthand is three Rs: rigorous, as in a standard randomised trial, but also rapid and regular. Using data already in government systems keeps the cost of each round low.
How research affects policy. An experiment with 2,150 Brazilian municipalities found that mayors will pay to learn research results, and that telling them about evidence on tax reminder letters made adoption of the policy more likely. Angrist cites it as an example of studying evidence uptake directly. Hjort, Jonas, Diana Moreira, Gautam Rao, and Juan Francisco Santini. 2021. "How Research Affects Policy: Experimental Evidence from 2,150 Brazilian Municipalities." American Economic Review 111 (5): 1442-80. Angrist also describes a forthcoming experiment in Bangladesh that showed policymakers different kinds of evidence; early results suggest global causal evidence carries more weight than many assume.
Second-best policy. If the best policy is politically impossible, a workable alternative that still improves learning may be the better target. Angrist credits Stefan Dercon and Lant Pritchett with making this case. Part of the problem is visibility; a new school is easy to point at, and learning is rarely measured clearly.
Outcomes funding. Funders pay providers for measured results, such as learning gains, rather than for inputs. The What Works Hub is studying two schemes: the Ghana Education Outcomes Project and the Sierra Leone Education Innovation Challenge, an $18 million programme across 325 schools from 2022 to 2025.
The policy-practice gap. During COVID-19, governments adopted radio, television and phone-based teaching. Angrist and Dercon matched government policy data to household surveys to see who received it. Angrist says nearly all governments adopted new distance education policies, but just over 20% of households in Sub-Saharan Africa and about half in the Middle East and North Africa received them. Latin America did far better. Angrist, Noam, and Stefan Dercon. 2024. "Mind the Gap between Education Policy and Practice." Nature Human Behaviour 8 (12): 2261-63.
Difference-in-differences at scale. Once a programme reaches every school, there is no control group for a randomised trial. Difference-in-differences compares changes over time between groups. Comparing districts or schools that did and did not get a programme does not work after a national rollout; comparing a cohort that received it with an earlier cohort that did not still does. Angrist says a recent review he worked on found more than 65% of such studies in education use the location design.
Tusome. Kenya's national literacy programme, a structured pedagogy approach scaled to every public primary school from 2015. It improved learning at scale, but its effects did not last as many hoped. Piper, Benjamin, et al. 2018. "Scaling Up Successfully: Lessons from Kenya's Tusome National Literacy Program." Journal of Educational Change 19 (3): 293-321.
Teaching at the right level in Uttar Pradesh. The approach, developed by the Indian NGO Pratham, was refined over years of randomised trials before government scale-up. Angrist says the Uttar Pradesh rollout reached more than five million children in over 100,000 schools, and that a new quasi-experimental evaluation finds it worked. The earlier scale-up trials: Banerjee, Abhijit, Rukmini Banerji, James Berry, Esther Duflo, Harini Kannan, Shobhini Mukerji, Marc Shotland, and Michael Walton. 2017. "From Proof of Concept to Scalable Policies: Challenges and Solutions, with an Application." Journal of Economic Perspectives 31 (4): 73-102.
More VoxDev Talks episodes

The gap between education policy and practice. Angrist's previous visit, on the COVID-19 data behind the policy-practice gap.
Schools are failing to deliver learning. Lant Pritchett on why schooling is not education, the conversation Tim refers to at the start of this episode.
Increasing learning at scale in Ghana. Adrienne Lucas on testing four learning programmes at scale with the Ghanaian government.
Related reading on VoxDev

Implementation matters: Measure it and account for it. Noam Angrist and Rafe Meager show that implementation explains most of the variation in the effects of targeted instruction across studies.
Educating children in emergencies: Global evidence from five randomised trials. Evidence on low-cost phone tutoring tested across five countries.

In many cities in low-income countries, the grid fails often enough that businesses keep a diesel generator out the back. So an unreliable electricity grid looks like it is holding poor economies back. In many countries, lenders are putting money behind that idea.
But Martin Shu and his co-authors, Jonathan Colmer and David Lagakos, set out to test it. They assembled data on power plants, fuel, workers and imported generators in 89 countries, and measured how productive each electricity sector was. In the poorest countries, electricity was about three-quarters as productive as in the US — in other words, much closer tot he frontier than their economies. And in the economic model they built using their data, bringing every country up to the world frontier adds only about 1% to long-run GDP.
Shu presented the research at STEG's sixth Annual Conference in Nairobi in January 2026. He tells Tim Phillips where the productivity gap in electricity lies, why a shoe factory that is better at left shoes than right shoes explains the small gains, and which part of the economy is the real bottleneck.
The research behind this episode

Colmer, Jonathan, David Lagakos, and Martin Shu. 2026. "Is the Electricity Sector a Weak Link in Development?" Working paper, January 2026 version presented at the STEG Annual Conference, Nairobi. An earlier version appeared as NBER Working Paper 32041 (2024).
To cite this episode

Phillips, Tim, and Martin Shu. 2026. "Is electricity a weak link in development?" Conversations on Transformation (podcast).
About the guest

Martin Shu is Assistant Professor of Economics at the School of Management and Economics and the Shenzhen Finance Institute of the Chinese University of Hong Kong, Shenzhen. His research spans macroeconomics, development and labour economics, including what household and firm data reveal about structural transformation, and why children in poor countries are more likely to follow their parents into the same occupation. He holds a PhD in Economics from Boston University and bachelor's and master's degrees from the Hong Kong University of Science and Technology.
Research cited in this episode

Weak links are sectors whose problems hold back the whole economy. When inputs are strong complements, output depends heavily on the least productive link in the chain, so a small sector can matter far more than its size suggests. The idea draws on Albert Hirschman's The Strategy of Economic Development (1958), and Charles Jones formalised it in "Intermediate Goods and Weak Links in the Theory of Economic Development" (American Economic Journal: Macroeconomics, 2011), which uses electricity as a motivating example. Shu and his co-authors ask whether electricity fits that description in poor countries today.
Total factor productivity (TFP) measures how much output an economy or a sector gets from its inputs. If two countries have the same capital and the same number of workers, but one produces more, it has higher TFP. Shu measures each country against the United States. The figures for whole economies come from the Penn World Table, hosted by the Groningen Growth and Development Centre and described by Robert Feenstra, Robert Inklaar and Marcel Timmer in "The Next Generation of the Penn World Table" (American Economic Review, 2015). The paper uses version 9.1; the current release, PWT 11.0, is supported by STEG.
Agriculture's productivity gap is the comparison Shu uses to show why measuring TFP is not enough. Farming in poor countries is far less productive than the rest of the economy, as Francesco Caselli ("Accounting for Cross-Country Income Differences," Handbook of Economic Growth, 2005) and Diego Restuccia, Dennis Tao Yang and Xiaodong Zhu ("Agriculture and Aggregate Productivity: A Quantitative Cross-Country Analysis," Journal of Monetary Economics, 2008) document. Farmers are also the majority of workers in many developing countries. Yet few economists call agriculture a weak link. Whether a sector is a bottleneck depends on how it connects to the rest of the economy, and answering that needs a model as well as data.
The electricity data combine several sources. Generating capacity comes from S&P Global Platts' World Electric Power Plants database, which lists more than 200,000 plants; the authors use generating capacity alone because it tracks transmission and distribution capacity closely. Power output and fuel use come from the International Energy Agency, and employment from national statistics offices. To count power from private generators, the authors use imports of generators recorded in the UN Comtrade database, an approach inspired by Francesco Caselli and Daniel Wilson ("Importing Technology," Journal of Monetary Economics, 2004). It works because few poor countries make their own generators. On the authors' conservative measure, generators supply about 7.6% of capacity on average.
Labour's share of revenue in electricity is about 7%, in rich and poor countries alike. The authors collected annual reports, financial statements and SEC filings for 69 privately owned electricity companies in 31 countries, choosing private firms because their decisions follow profit rather than government mandate. Labour's share shows no relationship with GDP per capita. A share that does not change with income points to a Cobb-Douglas production function, in which each input's share of costs stays constant, and that simplifies the TFP calculation.
Transmission and distribution losses are power that leaves a plant but never reaches a customer, lost as heat in wires and transformers, or stolen. According to IEA data, they average 14% of output across the sample, 22% in the poorest quarter of countries and 7% in the richest. They are the strongest predictor of low electricity TFP; once they are taken into account, the link between electricity TFP and national income largely disappears. Shu points to upgraded transformers close to end users, and ultra-high-voltage transmission lines, as the investments that would close the gap.
Complementarity describes inputs that work together and cannot easily replace each other, like left and right shoes. The model sets the elasticity of substitution between electricity and everything else at 0.2, following Ernst Berndt and David Wood ("Technology, Prices, and the Derived Demand for Energy," Review of Economics and Statistics, 1975). Strong complementarity sounds as if it should make electricity more important. Shu's shoe factory shows why it does not: when a sector is already efficient, making it more efficient frees few resources, and output still waits on the less productive partner.
Hulten's theorem, from Charles Hulten's "Growth Accounting with Intermediate Inputs" (Review of Economic Studies, 1978), predicts the economy-wide gain from a productivity improvement in one sector: multiply the improvement by the sector's Domar weight, its sales as a share of GDP. The authors treat any gain above that prediction as the sign of a weak link. Raising electricity TFP to the world frontier, defined as the 90th percentile, means an average increase of 43%, and by Hulten's rule it would add 1.7% to GDP. The model delivers about 1%, and only six countries beat the benchmark. The biggest exceptions are Ethiopia and Kenya, where frequent outages make power expensive or halt production. The authors also test their results against David Baqaee and Hannes Malmberg's "Long-Run Comparative Statics" (NBER Working Paper 33504, 2025), which extends Hulten's approach to allow for capital accumulation.
Raising productivity outside electricity is the counterpart experiment. When the authors raise TFP in the rest of the economy by the same proportion instead, every country gains more than Hulten's theorem predicts, and the capital stock grows by 75% on average. Shu's conclusion is about balance. With complementary sectors, pushing one to an extreme achieves little, and today it is the non-electricity sector that lags.
More Conversations on Transformation episodes

A Microeconomic Perspective on Misallocation. Eric Verhoogen explains how economists diagnose the wedges that keep resources from their best use, the same kind of distortion Shu's model uses to capture outages and costly self-generated power.
Structural change in sub-Saharan Africa. Gaaitzen de Vries and Kei-Mu Yi ask whether African economies follow the familiar path of structural transformation, a wider view of the sectors that Shu argues are holding growth back.
Further reading

Can Mass Electrification (Still) Cause Structural Change?, a STEG synthesis paper by Eric Hsu and Mitchell VanVuren, reviews the mixed evidence on whether connecting people to power still raises productivity and incomes in low- and middle-income countries, as it appears to have done in the past.
Under the Grid: Price and Informational Barriers to Grid Densification in Benin, a STEG working paper by Arnaud Dakpogan, Megan Lang and Alpha Ly, finds that a connection subsidy did not raise formal connection rates on average, but information on costs and procedures nearly doubled them among households with no connection at all.

King Leopold II of Belgium told his envoy in London that he did not want to lose his slice of "this magnificent African cake". The cake was the Congo Free State. Today the Democratic Republic of Congo holds 70% of the world's cobalt reserves, and so the cake is back on the table.
Christopher Adam (Oxford) is one of the editors of a special issue of the Oxford Review of Economic Policy on the new scramble for critical minerals. The minerals lie mostly in the Global South, and the demand comes mostly from the North. In this week's VoxDev talk, Chris explains why a mining boom may create few jobs, why it might not last, and why hiring the best lawyers could be the smartest way to use an aid budget.
The research behind this episode:
Adam, Christopher, Rabah Arezki, and Frederick van der Ploeg. 2026. "The scramble for critical minerals." Oxford Review of Economic Policy 42 (1): 1-13. Open access. The introduction to Volume 42, Issue 1, a special issue on critical minerals.
To cite this episode:
Phillips, Tim, and Christopher Adam. 2026. "The critical minerals scramble.” VoxDev Talks (podcast). 

About the guest

Christopher Adam is Professor of Development Economics at the Oxford Department of International Development, University of Oxford. He is managing editor of the Oxford Review of Economic Policy, an associate editor of the Journal of Development Economics, a Lead Academic for the International Growth Centre, and a Visiting Scholar at the International Monetary Fund. His research spans the macroeconomics of low-income countries, monetary economics and public finance, and growth and structural change, including the response to climate change and natural disasters.
Research cited in this episode

Leopold II and the "magnificent African cake". The opening quotes a letter from King Leopold II of Belgium to his envoy in London, in the English translation used by Adam Hochschild in King Leopold's Ghost (Houghton Mifflin, 1998). Leopold went on to rule the Congo Free State as a personal possession. Chris uses the comparison to ask whether today's scramble will end any better for the people who live on top of the minerals.
What makes a mineral critical. There is no single list. The usual working definition, from the US National Research Council (2008), is that a mineral must be both essential to a modern technology and subject to supply chain risk. In the same special issue, geologist Jon Blundy compares the critical mineral lists of 12 countries and finds that only lithium and the rare earths appear on all of them.
Demand to 2040. The International Energy Agency (IEA 2021) projects that demand for minerals for clean energy technologies will rise at least fourfold by 2040 if the world meets its climate goals. Chris adds two further sources of demand, digital infrastructure and defence.
China's grip on processing. Mining is spread across many countries; refining is not. China controls between 60% and 80% of final global supply of processed critical minerals (Leruth et al. 2022, cited in the paper). Chris argues this concentration is what makes the current scramble different from the earlier one for oil and gas.
The presource curse. A term from World Bank economist James Cust and David Mihalyi (IMF 2017). Governments and citizens start spending in anticipation of a resource boom, before any revenue arrives, and growth can fall as a result. Chris warns against the same over-exuberance about local processing of critical minerals.
Battery substitution. Lithium-ion batteries dominate today, but sodium-based alternatives are in development (Vu 2025, cited in the paper). High prices raise the incentive to find substitutes, so a producer country cannot assume today's price will hold.
Take-or-pay contracts. In a take-or-pay contract, the buyer pays for a minimum quantity of output whether or not it takes delivery. The paper proposes such long-term contracts, used in natural gas, as one way to share the risk of technological change between mining companies and producer governments.
Taxing value that sits downstream. In the special issue, Gregoire Rota-Graziosi argues that the rent from critical minerals is moving away from the mine and towards processing plants and intangible assets. His proposals include anchoring prices to international benchmarks to limit transfer pricing abuse. Chris stresses the role of royalties.
Indonesia's nickel export ban. Indonesia banned exports of raw nickel ore from 2020. It is now the world's leading nickel producer and processor, but the paper notes that the main impetus came from Chinese firms and investment in industrial parks. Chris raises it as a success with a caveat.
The double dividend. In the special issue, Mathieu Couttenier and Dominic Rohner argue that the green transition could reduce conflict as well as emissions, if governance, transparency and multilateral institutions are strong enough. Chris says he would like to share their optimism.
Dutch disease. A resource boom drives up the real exchange rate and makes other exports less competitive (Eastwood and Venables 1982). Because mining creates few jobs, Chris argues that industrial policy beyond the mining sector must address this risk directly.
More VoxDev Talks episodes

No taxation without administration: What makes tax authorities work. Royalties and transfer pricing rules are only as good as the tax authority that enforces them.
Rethinking development cooperation: The case for a 'balance sheet' approach. A proposal to treat low and middle-income countries as managers of their own assets, which is the position a mineral-rich government is in.
Related reading on VoxDev

Mining booms move workers from farms to services, not factories, by Qing Huang, Victoria Wenxin Xie and Wei You. Evidence from 33,262 mines on what resource booms do to local employment.
Who owns the mine matters for deforestation, by Victoria Wenxin Xie, Wei You and Ran Goldblatt. Mineral price booms increase deforestation near mines, and investor origin changes the size of the effect.
The downstream impacts of mines: How pollution hits agriculture, by Lukas Vashold, Gustav Pirich, Maximilian Heinze and Nikolas Kuschnig. In Africa, crops are less healthy downstream of mining sites.

This is an episode from VoxDev's new podcast series, Ideas in Development. This series has a separate podcast feed, where you can find every episode of Oliver Hanney’s conversations on evidence.
YouTube: https://www.youtube.com/watch?v=R8eCnQy5fF4 
Apple Podcasts: https://podcasts.apple.com/us/podcast/givedirectlys-quest-for-scale/id1866874059?i=1000791048981 
Spotify: https://open.spotify.com/episode/2ffbhYkt9bYNiWUc5KPIuZ?si=13787b330c604508 
Audioboom: https://audioboom.com/posts/8955404-givedirectly-s-quest-for-scale 
GiveDirectly started out as a small nimble team founded by PhD economists, who had a novel approach to ending poverty – just give cash. But they are no longer the new kids on the block, and have been scaling their operations rapidly in recent years, a trend that could intensify if the third wave of American philanthropy materialises.
That’s a huge opportunity, but the potential of operating across entire countries is a radically different proposition. So what does an evidence-driven organisation research when it's trying to go from moving millions a year to billions?
Caitlin Tulloch, Senior Director for Research, Learning and Product at GiveDirectly, joins Oliver Hanney for a wide-ranging conversation on cash transfers at scale. We cover running a research portfolio like the treasury, the macro forecasting work around a new Malawi project, the trade-off between fraud and reach, building a global emergency response capability, and the politics of putting a lot of cash into someone else's economy.
Ideas in Development is a VoxDev podcast on economic policy and research. Find us wherever you get your podcasts, and read the full write-up on our Substack: https://ideasindevelopment.substack.com/

Medicine has run rigorous clinical trials since the 1940s. Development economists borrowed the structure of the trials during the credibility revolution. Chris Cotton (Queen's University) argues that they misunderstood an important part of this revolution. One successful study is not a mature evidence base, and policies built on too little evidence tend to disappoint at scale. 
His answer is a framework of Policy Evidence Readiness Levels, or PERLs, just published in Science. PERLs 1 through 4 categorise the weight of evidence behind an intervention, and are inspired by the scale NASA uses to judge whether a technology is ready for a space mission. He tells Tim Phillips which development programmes have already climbed to the top rung, which were implemented at scale on too little evidence (and what happened when they were), and why his framework, by his own admission, is still a modest PERL level 1.
The research behind this episode

Cotton, Christopher. 2026. "Rigor Is Not Readiness: The PERL Framework for Evidence-Based Policy." Science 393 (6810): 463-465.
To cite this episode

Phillips, Tim, and Christopher Cotton. 2026. "Evidence-based policy: Why one good trial isn't enough." VoxDev Talks (podcast).

About the guest

Christopher Cotton is Professor of Economics at Queen's University in Kingston, Ontario, where he holds the Jarislowsky-Deutsch Chair in Economic and Financial Policy and directs the John Deutsch Institute for the Study of Economic Policy. He is cross-appointed to the School of Policy Studies and the Department of Medicine. His research spans evidence-based policy, the economics of science, education and public health, and how organisations use expertise when they make decisions. He is a co-owner of and research adviser at Limestone Analytics, a policy advisory firm, and has advised on impact evaluation and evidence-based policy for the UK and US governments, the World Health Organization, and others.
Research cited in this episode

Evidence-based medicine. The movement that took hold in the 1990s, decades after the clinical trial became standard. Its classic statement is Sackett, David L., William M. C. Rosenberg, J. A. Muir Gray, R. Brian Haynes, and W. Scott Richardson. 1996. "Evidence Based Medicine: What It Is and What It Isn't." BMJ 312 (7023): 71-72. It set out how clinicians should combine the best research evidence with clinical judgement. Cotton's point is that medicine's evidence hierarchy puts systematic reviews above any single trial; the social sciences adopted the trials but not the hierarchy.
Technology Readiness Levels. NASA's nine-level scale for the maturity of a technology, from basic principles observed (TRL 1) to flight proven on a successful mission (TRL 9). It gives engineers a shared vocabulary for readiness without dictating how each component is tested. PERLs borrow the idea and apply it to claims about policy.
The four PERLs. PERL 1 is a hypothesis, backed by theory or observational data. PERL 2 is efficacy, shown in controlled trials under favourable conditions. PERL 3 is targeted adoption, with at least one rigorous causal evaluation under real-world implementation. PERL 4 is generalised guidance, built on systematic reviews that address how effects vary across contexts. Cotton's examples of PERL 4 evidence in development include insecticide-treated bed nets for malaria, cash transfers for school enrolment, and iron and folic acid supplements for pregnant women.
The science of scaling. A growing literature on why promising pilots disappoint at scale; Cotton cites Rasul, Imran. 2026. "From Field Experiments to Policy Interventions at Scale." Science 391 (6790). Much of this work asks researchers to test programmes under real-world conditions. In PERL terms, that moves evidence from level two to level three; Cotton argues it is necessary but not sufficient.
Evidence synthesis organisations. Cochrane produces systematic reviews in health; the Campbell Collaboration does the same for social policy; 3ie, the International Initiative for Impact Evaluation, funds and synthesises impact evaluations in development. Together with J-PAL's evidence reviews and WHO guidelines, Cotton identifies them as where PERL 4 evidence lives.
Microcredit. Cotton's main cautionary tale. Early pilots produced promising causal evidence under specific conditions, and donors, NGOs, and the media turned it into a claim that microcredit would transform global poverty. The later randomised evidence is summarised in Banerjee, Abhijit, Dean Karlan, and Jonathan Zinman. 2015. "Six Randomized Evaluations of Microcredit: Introduction and Further Steps." American Economic Journal: Applied Economics 7 (1): 1-21. Across six countries, the studies found some increase in business activity but no evidence of a reduction in poverty.
The graduation approach. A package of a productive asset, training, coaching, savings, and consumption support for ultra-poor households, first developed by the Bangladeshi NGO BRAC in 2002. The landmark multi-country study is Banerjee, Abhijit, Esther Duflo, Nathanael Goldberg, Dean Karlan, Robert Osei, William Parienté, Jeremy Shapiro, Bram Thuysbaert, and Christopher Udry. 2015. "A Multifaceted Program Causes Lasting Progress for the Very Poor: Evidence from Six Countries." Science 348 (6236): 1260799. J-PAL's Policy Insight now draws on 20 randomised evaluations. Cotton uses it as an example of evidence that matured as implementation expanded.
The reading wars. Cotton's example from outside development. Many education systems adopted whole-language and three-cueing approaches to reading, based on appealing theory and small, heavily resourced studies, and pushed phonics aside. The evidence is reviewed in Castles, Anne, Kathleen Rastle, and Kate Nation. 2018. "Ending the Reading Wars: Reading Acquisition from Novice to Expert." Psychological Science in the Public Interest 19 (1): 5-51.
Quasi-experimental methods. Techniques such as difference-in-differences, which compare changes over time between places or groups that did and did not receive a policy. Cotton argues that macro policies and institutional reforms, which cannot be randomised, can still climb to PERL 3 and even PERL 4 by combining such studies with well-tested theory and the historical record.
More VoxDev Talks episodes

How do policymakers interpret different types of evidence? Eva Vivalt on how policymakers update their beliefs when they see new evidence, and the biases that get in the way.
Rethinking evidence and refocusing on growth in development economics. Lant Pritchett makes the sceptic's case against relying on RCTs and systematic reviews as the main guide to policy.
How AI can put 20 years of development evidence to work. Iqbal Dhaliwal of J-PAL on building AI programmes on the existing evidence base, and the scaling problems AI inherits.
Related reading on VoxDev.org

Scaling policy ideas in developing countries, in which John List argues that researchers should generate policy-based evidence before decision-makers commit to scale.
Insights from first generation of microcredit RCTs, from the VoxDevLit on microfinance, which reviews seven randomised evaluations of microcredit programmes.