Comments on 'Covariance Adjustments for the Analysis of Randomized Field Experiments'

Richard Berk, Emil Pitkin, Lawrence Brown, Andreas Buja, Edward George, and Linda Zhao (2014) have written a valuable Evaluation Review paper on regression adjustment in randomized experiments. I’ve long been a fan of Berk’s critical writings on regression and meta-analysis (Berk 2004, 2007; Berk and Freedman 2003), and I recently recommended Berk, Brown, et al.’s (2014) helpful Sociological Methods and Research paper to a colleague teaching a course on regression. Also, I am grateful to Berk for sending me kind and constructively critical comments on Lin (2013) after it went to press. In my reply to his e-mail, I shared an informal essay (Lin 2012a, 2012b) discussing regression adjustment in practice. We are in agreement on many points.