In the last decade or so, researchers have published a number of very high-quality randomized trials and quasi-experiments. Rigorous study of programs like Alcoholics Anonymous is challenging because people self-select into them. Unless a study is carefully designed, its results can be driven by who participates, not by what the program does. Even randomized trials can succumb to bias from self-selection if people assigned to A.A. don’t attend, and if people assigned to the control group do. (It may go without saying, but we’ll say it: It would be unethical to prevent people in a control group from attending Alcoholics Anonymous if they wanted to.)

Source: New York Times March 11, 2020 11:00 UTC