Statistical notes for clinical researchers: analysis of covariance (ANCOVA)

Abstract

Previously, we discussed analysis of variance (ANOVA) and simple linear regression, which commonly share continuous dependent variables. While ANOVA uses categorical variables as independent variables, regression uses mainly continuous variables for them. However, we may want to include both kinds of variables in analysis. A statistical model with continuous dependent variables and both types of independent variables is called a general linear model (GLM). In this section, we discuss analysis of covariance (ANCOVA) as a type of GLM models. An ANCOVA is similar to an ANOVA model, but it includes a continuous variable as well as categorical variables as independent variables, being a mixture model of ANOVA and regression models.