Analysis of covariance
Analysis of Covariance (ANCOVA) is a statistical method which is an extension of ANOVA that provides a way of statistically controlling the linear effect of variables one does not want to examine in a study. These extraneous variables are called covariates, or control variables. Covariates should be measured on an interval or ratio scale. ANCOVA, which combines regression analysis and analysis of variance (ANOVA), controls for the effects of covariate(s). There should be no multicollinearity between covariates. On the other hand there should be a linear association between dependent variable and covariate(s). If a good covariate is used in ANCOVA, then type 2 error decreases, in other words the power of the study increases.
Key words: ANOVA, linear regression, covariate