https://www.youtube.com/watch?v=2x4fMW7WaC4 The Frisch-Waugh-Lovel theorem is a well-known result in theoretical economics. The theorem goes back to the 1933 paper of Frisch and Waugh. In this paper, they consider regressing an outcome variable on several covariates and a linear trend. They are interested in cancelling out the time trend from both outcome and covariates. What they show…