[Eeglablist] Over-inflated degrees of freedom

Marco Montalto montaltomarco at onvol.net
Fri Oct 31 12:46:04 PDT 2014

Dear List,

I have conducted a study in which 20 participants (10 female and 10 male) were tested during 2 conditions using 32 electrodes placed on the scalp. I ran a mixed model ANOVA with within-subject factors condition (2 levels) and electrode (32 levels) and between-subject factor gender (2 levels). I got no significant main effects or interaction terms and therefore I collapsed across electrodes. Now each subject was represented by 32 values and therefore the degrees of freedom looked funny (they were huge) but the results were exactly as expected. If I took an average of each 32-value-cluster, again, I lost all significance. Does the method of having each subject represented by 32 values seem sensible to anyone and, if not, can anyone suggest a different method of analysis I could adopt?

Thanks in advance for any advise/suggestions!


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