Editing Analysis of covariance (section)

==Power considerations==
While the inclusion of a covariate into an ANOVA generally increases [[statistical power]]<ref>{{cite journal |last1=Barrett |first1=Timothy J. |title=Computations using analysis of covariance |journal=WIREs Computational Statistics |date=2011 |volume=3 |issue=3 |pages=260–268 |doi=10.1002/wics.165 |url=https://wires.onlinelibrary.wiley.com/doi/abs/10.1002/wics.165 |language=en |issn=1939-0068|url-access=subscription }}</ref> by accounting for some of the variance in the dependent variable and thus increasing the ratio of variance explained by the independent variables, adding a covariate into ANOVA also reduces the [[Degrees of freedom (statistics)|degrees of freedom]]. Accordingly, adding a covariate which accounts for very little variance in the dependent variable might actually reduce power.