dear all,
i am running second-level analyses in spm 8, using the 'flexible factorial' design with the two built-in factors 'repl' and 'subject'. four conditions, as given by four images (four conditions) for each subject—that just works fine, so far, so good, nice results.
i now want to include a covariate in the model, with a single number for each subject (=a digit span measure). i included my digit span vector (one value for each subject) as a covariate in the model, such that i repeat each entry of the vector four times (four conditions), using 'kron' or 'reshape' or whatever.
the models runs through nicely, but my covariate does not have any effect, i.e. all values (p, z, etc.) stay identical—i wonder why this is the case, and i am very happy about any suggestions!
thanks,
l.
(ps: is it so that the covariate (which is now identical for each condition, since i replicated the original vector) cancels itself out in any contrast i specify? e.g. if i go for '-1 1 -1 1', the associated covariates cancel each other out?)
Lars Meyer | MSc
Max Planck Institute for Human Cognitive & Brain Sciences
Department of Neuropsychology
Stephanstraße 1a
04103 Leipzig
Office | +49 (0)341 99 40 22 66
Fax | +49 (0)341 99 40 22 60
Mobile | +49 (0)175 113 76 65
Home | +49 (0)341 974 26 49
Mail | [log in to unmask]
Web | www.cbs.mpg.de/~lmeyer
|