What is ANCOVA?

ANCOVA stands for analysis of Covariance", a general linear model with a continuous outcome variable (quantitative, scaled) and two or more predictor variables where at least one is continuous (quantitative, scaled), and at least one is categorical (nominal, non-scaled).  The Analysis of Covariance is often used when comparing groups in a quasi-experimental research study.  ANCOVA allows for the comparison of groups while controlling for one or more factors (covariate).  For example, we can compare post-test scores between the treatment and control group while controlling for any differences in pre-test scores.