In this blog post, incoming faculty Pam Jakiela brings us back to those metrics classes with a discussion of just what "difference in differences" is really doing.
If you've gotten a little rusty on your diff-in-diffs, want to see a different explanation, or want to think a little more carefully about just what assumptions are in play when you're using these methods, or reading an article where someone has used these methods, this is a great read.
Thanks to Prof. Shore-Sheppard for the recommendation!