Covariates are commonly used as control variables. For instance, use of a baseline pre-test score can be used as a covariate to control for initial group differences on math ability or whatever is being assessed in the ANCOVA study.

What does a covariate do?

A covariate is thus a possible predictive or explanatory variable of the dependent variable. This may be the reason that in regression analyses, independent variables (i.e., the regressors) are sometimes called covariates. Used in this context, covariates are of primary interest.

When should I run ANCOVA?

ANCOVA is a type of general linear model (GLM) that includes at least one continuous and one categorical independent variable. ANCOVA is useful when the effect of experimental conditions is important while there is an additional continuous variable in the study.