Identification of Confounding versus Dispersing Covariates by Confounding Influence

As is well known, omission of non confounding covariates identified by the treatment assignment may lead to considerable bias for estimated treatment effect even in a simple randomized trial. In this article we identify confounding vs. dispersing covariates by the confounding influence characterizing variance change and bias risk of estimated treatment effect due to constraint on effects of these covariates. Consequently, consistent constraint on effects of identified confounding covariates reduces variance of estimated treatment effect whereas inconsistent constraint on effects of identified dispersing covariates—such as omission of identified dispersing covariates—leads to little bias for estimated treatment effect.