Analysis of covariance (ANCOVA) is a
general linear model which blends
ANOVA and
regression. ANCOVA evaluates whether population means of a
dependent variable (DV) are equal across levels of a categorical
independent variable (IV) often called a treatment, while statistically controlling for the effects of other continuous variables that are not of primary interest, known as
covariates (CV) or nuisance variables. Mathematically, ANCOVA decomposes the variance in the DV into variance explained by the CV(s), variance explained by the categorical IV, and residual variance. Intuitively, ANCOVA can be thought of as 'adjusting' the DV by the group means of the CV(s).