With respect to calculating the epsilon index of sphericity for ANOVA, 
discussed on pp. 45-47 of:

http://www.psych.upenn.edu/~baron/rpsych.pdf

It notes that epsilon is not required for a repeated measures design with 
only k=2 levels, as the minimum value of epsilon (e) is given by:

e = 1/(k-1)

so for k=2, we have e = 1 (ie, no correction of the F test df; see p. 46). 
These notes apply to a univariate F test.

How do we estimate the minimum value of epsilon for a 2 factor ANOVA?

I have an experiment where we measure brain activity from the left and right 
hemisphere, for two experimental conditions, in each subject. I consider the 
measures from each hemisphere a repeated measures factor (2 levels) and the 
experimental conditions is also a repeated measure (2 levels). The question 
now is, how do we calculate epsilon for this 2 factor study and is it 
possible that epsilon could be anything < 1 when each factor has only 2 
levels?

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