Estimation of the Box Correction for Degrees of Freedom from Sample Data in Randomized Block and Split-Plot Designs

It has been suggested that when the variance assumptions of a repeated measures ANOVA are not met, the df of the mean square ratio should be adjusted by the sample estimate of the Box correction factor, ɛ. This procedure works well when ɛ is low, but the estimate is seriously biased when this is not the case. An alternate estimate is proposed which is shown by Monte Carlo methods to be less biased for moderately large ɛ.