Sample size, or power calculations are an integral part of conducting randomised controlled trials. Rules of thumb can be useful in these calculations, but can have negative consequences if the rules do not match up with reality. We review a large database of effect sizes in education, and find...

Under-participation in selective universities lowers social mobility in England, the United States, and elsewhere. English universities have standardized tuition costs, and strongly heterogeneous graduate earnings. Attending a selective university is therefore strongly incentivized, yet...