If the dependent variable, math score (Y), is about the same for persons with higher scores in writing (X) and for those with lower scores in writing, one would expect that
A) adding the covariate will not substantially reduce error variation.
B) the adjusted mean for each group will be the same.
C) ANCOVA will be more powerful than ANOVA.
D) the covariate and factor will be independent of each other.

Question

Quizplus · Accepted Answer

Adding a covariate that does not vary systematically with the dependent variable will not substantially reduce error variation in the analysis. Since the math score is about the same for persons with higher and lower scores in writing, the writing score (as a covariate) is not expected to explain a significant portion of the variance in math scores, thus not reducing error variation substantially.

If the Dependent Variable, Math Score (Y), Is About the Same