Fifteen years ago, he began conducting meta-analyses of antidepressant drug trials. A meta-analysis is a statistical abstract of many individual drug trials, and the method is controversial. Drug trials are designed for different reasons—some are done to secure government approval for a new drug, and some are done to compare treatments—and they have different processes for everything from selecting participants to measuring outcomes. Adjusting for these differences is complicated, and Kirsch’s early work was roundly criticized on methodological grounds by Donald Klein, of Columbia University, who was one of the key figures in the transformation of psychiatry to a biologically based practice. But, as Kirsch points out, meta-analyses have since become more commonly used and accepted.