In: Statistics and Probability
Why does repeated measure ANOVA have larger power than between-subject ANOV?
A Repeated measure ANOVA is conducted when the results (with the same factor) of the same group have to be analyzed over a while. e.g In a study to understand the variation in cholesterol level amongst the same group of participants at 1,3, 6 months after changing their diet. Thus, for this study, the dependent variable would be cholesterol and the independent variable would time. Since the same set of participants are studied over a while, they act as a control group for themselves.
By conducting such a kind of experiment, the variance and bias of the model's error are controlled for the factors that generate variability between the subjects. (Note: The error terms in ANOVA constitute for errors within the subjects and not between the subjects). As the variation between the groups are controlled, the error term is reduced significantly.
Power in the ANOVA test is given by the probability of accepting the alternative hypothesis given it is true. Since there is lesser error term produced i.e. the difference between the subjects are under control, this test has larger power than between-subject ANOVA