For my thesis I need to calculate the sample size for an equivalence trial with four groups (the score on four equivalent forms in order to prove they are indeed equivalent). The study is done before with only one of the four forms, they found a mean = 19.8, SD = 2.0, tolerance = 1SD. I use an ANOVA to see whether they're significantly different.

Unfortunately, all I can find is programs for two groups or formulas I don't understand like this http://www.mddionline.com/article/determining-sample-size-testing-equivalence and this http://www.biostat.uzh.ch/teaching/master/previous/methods2008-1/4a_Equivalence.pdf (slide 17)..

For example the following:

n=2((Z1-a+Z1-b/2)^2)/((Delta-SD)^2)

This doesn't help me a lot, as I have no clue how to get Z(1-a)..

Anyone who could help me please?

Thanks a lot!!