Are ANCOVA Studies Better Than ANOVA Studies?
Our final warning [in Chapter 18] has to do with your general opinion of ANCOVA-based studies as compared with ANOVA-based studies. Because ANCOVA is more complex (due to the involvement of a larger number of variables and assumptions), many consumers of the research literature hold the opinion that data-based claims are more trustworthy when they are based upon ANCOVA rather than ANOVA. We strongly encourage you to refrain from adopting this unjustified point of view. Although ANCOVA (as compared with ANOVA) does, in fact, involve more complexities in terms of what is involved both on and beneath the surface, it is an extremely delicate instrument. To provide meaningful results, ANCOVA must be used very carefully–with attention paid to important assumptions, with focus directed at the appropriate set of sample means, and with concern over the correct way to draw inferences from ANCOVA’s F-tests. Because of its complexity, ANCOVA affords its users more opportunities to make mistakes t
