Regression to the mean and randomized control trials with continuous outcomes

Measurement errors in a study make the “regression to the mean” occur to different degrees. To remedy the “regression to the mean” effect in randomized control trials, one should measure the continuous outcome before randomization and adjust for the baseline outcome value in the analysis. This adjustment requires the use of regression constraints. The adjustment leads to lesser standard errors. After presenting a real case, I introduce the concept of “regression to the mean.” Then I introduce the relation from “regression to the mean” to the intraclass correlation and the measurement error. Using the case, I compare the estimates from several approaches in randomized control trials. Here I demonstrate the use of constraints. Knowing the intraclass correlation in power calculations will lead to a lesser required number of observations, for example, higher power. Hence, randomized control trials should report the intraclass correlation.