What is new and different about difference-in-differences?
Matt Bogard (noreply@blogger.com)
Back in 2012 I wrote about the basic 2 x 2 difference in difference analysis (two groups, two time periods). Columbia public health probably has a better introduction. The most famous example of an analysis that motivates a 2 x 2 DID analysis is John Snow's 1855 analysis of the cholera epidemic in London : (Image Source ) I have since written about some of the challenges of estimating DID with glm models (see here , here, and here.) , as well as combining DID with matching , and problems to watc