Control or overcontrol for covariates?

Covariate adjustment can adjust for baseline differences in randomised controlled trials (RCTs) that may have arisen by chance. Furthermore, even if the groups do not differ significantly on any factors, using baseline variables that may be related to the outcome as covariates can reduce the within-group variance, thus increasing the accuracy of the estimates of treatment effects and the power of the statistical test. However, improper use of …