In the typical repeated measures analysis, the subject effect is assumed to be random and the error terms random and uncorrelated. (One could assume that the subject effect is fixed while the errors are correlated.) In many statistical packages, unless the user specifically requests that otherMean Squares be used for tests, the MSE is used by default. A simulation study investigates the magnitude of the errors that result if the inappropriate tests are performed. It is found that both the Type I and Type II errors can be greatly affected