My research design is 2(Ear) x 3(Factor A) x 3(Factor B) with repeated measures on all factors. For 2 way-repeated ANOVA, I used laterality index (normal distribution, calculated from % of responses from both ears) as dependent variable (DV) while Factor A and B are independent variables (IV). I obtained significant main and interaction effects.
However, when I tried 3-way repeated ANOVA using % scores from each ear as DV, factor B becomes not significant. I'm not sure what could be wrong?
Is it because the % scores in one of the conditions were not normally distributed with p=0.041? The box plot looks alright but histogram has an inverted bell curve shape. I've tried log, square root and 1/x transformation but didn't work. Is it acceptable to run ANOVA since there's no equivalent non-parametric test in SPSS?
Could it be the way I run the test in SPSS? I followed exactly the same way as I did for 2-way repeated ANOVA because I couldn't find any examples similar to my research design. Most examples have a third between subject factor while mine are all within subject factors.
I'd really appreciate any help or suggestions because I'm confused and new with statistics. Many thanks.