I'm having a problem running a repeated-measures ANOVA in R using the
I have data from 18 subjects - each subject participated in 3 conditions, and data was collected in each subject/condition combination at 29 electrode sites (1566 total data points in a balanced design with no missing cells).
When I try to run the full ANOVA
model = ezANOVA(data, dv=voltage, wid=subject, within=.(electrode, channel))
I get the following error:
Error in lambda > 0 : invalid comparison with complex values Error in ezANOVA_main(data = data, dv = dv, wid = wid, within = within, :
The car::Anova() function used to compute results and assumption tests seems to have failed. Most commonly this is because you have too few subjects relative to the number of cells in the within-Ss design. It is possible that trying the ANOVA again with "type=1" may yield results (but definitely no assumption tests).
Things work fine though if I include fewer levels of
electrode than I have subjects (18 or fewer), but if I add more it fails. Why is this a problem? I wouldn't think that having greater-than-n levels for a within-subjects factor would be a problem if it's a balanced fully repeated-measures design. (SPSS will compute things just fine). Using Type I SS works, but if I select this option I won't give me the sphericity corrected p-values that I need to report.