We have randomly selected a sample of 10,000 people from the 2 million Americans with the coronavirus disease. To test a new treatment for COVID-19, we need to divide our sample into multiple groups.

In this paper, we consider what may be done when researchers anticipate that in the implementation of field experiments, random assignment to experimental and control groups is likely to be flawed. We ...

A key justification for using nonrandomized experiments is that, with proper adjustment, their results can well approximate results from randomized experiments. This hypothesis has not been ...

If our random sample (10,000 people diagnosed with COVID-19) took hydroxychloroquine and most recovered in a couple of weeks and only 5% needed to be hospitalized, can we conclude that ...