If my data are non-normally distributed and I'm conducting a 2x2 ANOVA, what can I do to correct for this problem so I can report the main effect and interaction output appropriately?
Only one finding is significant (one of the main effects). I've read that bootstrapping cannot be applied to a univariate ANOVA in SPSS...I also tried this out in SPSS myself and could not obtain any bootstrapped output.
I used a 2 x 2 (Age [6 years, 7 years] × Educational Classification [Group A, Group B]) univariate ANOVA to explore the hypothesis that test performance (percentage of items correct) would increase with age for children in Group B but would not differ significantly across age for students in Group A.
I transformed the percentages into arcsine values to meet the assumption of a continuous dependent variable.
My sample is small, so the sample size for each cell created by the 2 x 2 are as follows: Group A 6-year-olds = 10, Group A 7-year-olds = 13, Group B 6-year-olds = 20, and Group B 7-year-olds = 14.
I know that scores are non-normally distributed across Group A and across Group B due to most students obtaining high scores on the test (and I ran tests of normality and looked at the Q-Q plots). Group A, which is also the smaller group of the 2, has larger variance.
But should I run normality tests for all 4 groups created by the 2 x 2? I found a Main Effect for Educational Classification but not for Age, and there was no interaction.
I just want to know if my findings are valid given the non-normality, or if I should find a way to fix this problem in SPSS (e.g., bootstrapping).