Some of David Byar's work: in appreciation

David Byar wrote and thought with great clarity about randomized clinical trials (RCTs), pointing to their strengths--and to the limitations of alternative investigative approaches. An issue that he treated quite briefly in the seven publications that I review here is the possible gains to be had from post hoc covariate adjustment of RCT results. Calculations that I offer suggest that for realistic sample sizes and covariates of modest strength, those gains cannot be large, on average. The price to be paid for them is to replace the clear, cogent RCT paradigm with a more complex and diffuse one; this seems just cause for unease.