Dear Russ,
| > Andrew Holmes wrote:
| >
| > The key concepts for successful random effects analyses using the
| > random effects kit are:
| > (1) For inference to the population, it's the sampling of
| > subjects that matters most, not the number of scans/sessions
| > per subject.
| > (2) For valid population inference using the random effects
| > kit, you cannot have more than one scan per subject per
| > condition. (Strictly speaking you should only enter two
| > conditions too.)
|
| could you expand upon this last point about two conditions? Is this related
| to sphericity assumptions that are necessary for >2 conditions, or some
| altogether different issue?
It's due to sphericity assumptions, which are more than likely not met,
resulting in an artificially inflated degrees of freedom when naively
assessing more than two conditions in such a model.
-andrew
+- Dr Andrew Holmes [log in to unmask]
| -___ __ __ Wellcome Department of Cognitive Neurology - |
| ( _)( )( ) Functional Imaging Laboratory, Stats & |
| ) _) )( )(__ 12 Queen Square, Systems |
| (_) (__)(____) London. WC1N 3BG. England, UK |
+---------------------------------------http://www.fil.ion.ucl.ac.uk/-+
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