The backlash against randomised trials in policy has begun. Randomised controlled trials (RCTs) are widely accepted as the foundation for evidence-based medicine. Yet a decade ago, they were extremely rare in other contexts such as economics, criminal justice or social policy. That is changing.

In the UK, Downing Street’s newly privatised Behavioural Insight Team has made it cool to test new ideas for conducting policy by running experiments in which many thousands of participants receive various treatments at random. The Education Endowment Foundation, set up with £125m of UK government money, has begun 59 RCTs involving 2,300 schools. In the aid industry, RCTs have been popularised by MIT’s Poverty Action Lab, which celebrated its 10th anniversary last summer – one estimate is that 500 RCTs are under way in the field of education policy alone.

With such a dramatic expansion of the use of randomised trials, it’s only right that we ask some hard questions about how they are being used. The World Bank’s development impact blog has been hosting a debate about the ethics of these trials; they have been criticised in The New York Times and in an academic article by economists Steve Ziliak and Edward Teather-Posadas.