Difference-in-Difference
The Difference-in-Difference (DiD) analysis is a powerful econometric tool with very practical uses. The classical use of DID is to analyze the difference between two groups after some sort of treatment. Say, for example, that you want to compare scores of a college entrance exam, the SAT, for two groups of students, one group that participated in an SAT prep course (the treatment group) and one group that did not (the control group) …