Treatment effects/differences ANCOVA

Should treatment-by-covariate interactions be found, either through a test of homogeneity in an adjusted analysis or through ANCOVA, then analysis usually proceeds by looking at treatment differences within subgroups. Plots of treatment effects with associated confidence intervals within these subgroups are useful in this regard. 

The name ANCOVA indicates that covariates are taken into account in the analysis. A covariate is a variable other than the main variable of interest. In the case of our ongoing example of examining decreases in SBP, subjects baseline SBP is likely to be of considerable interest. This technique of ANCOVA can be used to control statistically for baseline differences and to prevent them from skewing the results for the treatment effect. 

---