Chapter 5: Analysis of Covariance

The Analysis of Variance (ANOVA) Techniques described earlier are used to investigate differences between group means. These techniques are used when the effect of several categorical (independent) variables on a “continuous” (dependent) variable is to be revealed.

In this section, another analysis of variance technique, Analysis of Covariance (ANCOVA) will be examined. ANCOVA is a statistical process used to compare the means of a continuous (dependent) variable in two or more groups in order to eliminate or increase the effect of another continuous variable that affects the variable in question.

ANCOVA combines regression analysis and analysis of variance when measuring the difference between group means. In ANCOVA, the results of the analysis of variance are corrected for the linear relationship between the dependent variable and the covariate. The advantage of ANCOVA over other techniques is its ability to reduce the error variance in the result and to reveal group differences, taking into account other differences between subjects.