Randomized experiments commonly compare subjects receiving a treatment to subjects receiving a placebo. An alternative design, frequently used in field experimentation, compares subjects assigned to an untreated baseline group to subjects assigned to a treatment group, adjusting statistically...

In recent years, social scientists have increasingly turned to matching as a method for drawing causal inferences from observational data. Matching compares those who receive a treatment to those with similar background attributes who do not receive a treatment. Researchers who use matching...

Experimental researchers routinely use regression in order to control for pre-treatment covariates. This practice has become controversial in the wake of recent demonstrations showing that this type of regression is prone to bias in small samples. Bias may even remain when units are sampled from...