Factorial designs are widely used for studying multiple treatments in one experiment. While "long" model t-tests provide valid inferences, "short" model t-tests (ignoring interactions) yield higher power if interactions are zero, but incorrect inferences otherwise. Of 27 factorial experiments...

This paper examines the case for randomized controlled trials in economics. I revisit my previous paper "Randomization and Social Policy Evaluation" and update its message. I present a brief summary of the history of randomization in economics. I identify two waves of enthusiasm for the method...

Evidence for the short-term impact of early intervention on childhood health is weak and inconsistent. Using rigorous methods, careful hypothesis setting, and socioeconomic contextualisation, we examine the impact of an Irish home visiting programme on child health. The treatment provides...

In response to budget problems, many urban school systems reduced resources for getting students to come to school, like truancy officers. Chicago, for instance, went from 150 truancy officers down to, in 1991, a total of zero. Is that a good idea? We explore here the effects of increased...

The rising popularity of randomized controlled trials (RCTs) in development applications has come with continuing debates about the merits of this approach. The paper takes stock of the issues. It argues that an unconditional preference for RCTs is questionable on three main counts. First, the...

Nudge interventions have quickly expanded from academic studies to larger implementation in so-called Nudge Units in governments. This provides an opportunity to compare interventions in research studies, versus at scale. We assemble a unique data set of 126 RCTs covering over 23 million...

As the COVID-19 pandemic progresses, researchers are reporting findings of randomized trials comparing standard care with care augmented by experimental drugs. The trials have small sample sizes, so estimates of treatment effects are imprecise. Seeing imprecision, clinicians reading research...