In a randomized control trial, the precision of an average treatment effect estimator can be improved either by collecting data on additional individuals, or by collecting additional covariates that predict the outcome variable. We propose the use of pre-experimental data such as a census, or a...

The unemployment rate in France is roughly 6 percentage points higher for African immigrants than for natives. In the US the unemployment rate is approximately 9 percentage points higher for blacks than for whites. Commute time data indicates that minorities face longer commute times to work,...