Tim
Posts:
5
Registered:
10/23/13


Re: oneway repeated measures ANOVA with more levels than subjects
Posted:
Oct 23, 2013 5:01 PM


Hi Art,
also to you of course thanks a lot for the fast response. I put the color example above to explain the general kind of problem we are facing. We are in fact looking at different angles in a visual display, and recorded EEG data. Sorry for the confusion, I guess my attempt at simplifying things by coming up with an illustrative example was misleading.
Cheers Tim
On Wednesday, October 23, 2013 7:39:16 PM UTC+2, Art Kendall wrote: > I do not know what the software other than SPSS was, but you may want to > > check with a discussion list for that software. My guess is that you > > did not use specifications that said you had repeated measures. > > > > I can think of no reason that you cannot have more levels of repeat than > > number of cases. > > > > Times series is a particular kind of repeated measure and economists > > routinely use a single case. > > > > BTW color can be a nominal level variable but it can also be thought of > > an array along a spectrum ROYGBIV, so you depending on exactly what you > > have for color stimuli you may be able to put structure on your repeats. > > > > What syntax did you use in SPSS? > > > > Art Kendall > > Social Research Consultants > > > > On 10/23/2013 12:48 PM, Tim wrote: > > > Hi everyone, > > > > > > I have a quick question about a oneway repeated measures ANOVA in cases where the number of levels in a factor is larger than the number of subjects measured. Let me illustrate my question with a quick example: Say we presented 20 different colors in an experiment and recorded reaction times for every condition in 15 subjects (a total of 20*15=300 measurements). To my understanding, as we have 15 withinsubject measurements for every cell, this should work perfectly fine. > > > > > > Unfortunately, two of the statistics functions we tried using throw an error stating that the number of conditions is too large given the number of subjects (one seems to directly compare the two numbers, the other one computes negative df_error). However, the same kind of setting works just fine in SPSS (df1 = 19; df2 = 266). > > > > > > Is there any principled reason why above setting should be problematic in a repeatedmeasures ANOVA? My search for an explanation has so far not brought up any reason why the number of levels in a factor should not exceed the number of subjects if all observations have been measured (n_obs = n_sub * n_cond). > > > > > > > > > Thanks a lot in advance, looking forward to your answers > > > Tim > > >

