Marco Buiatti marco.buiatti at GMAIL.COM
Thu Nov 30 15:27:46 CET 2006

Dear FieldTrippers,

I have a question on the use and interpretation of Cluster
Randomization Analysis on ERPs. I analised the statistical difference
between 2 conditions (9 subjects, within-subjects design), and I
obtained two NON-significant clusters, one negative in the frontal
lobe (p=0.24) and one positive in posterior regions (p=0.08). These
clusters emerge and die at almost the same times, so they really look
like reflecting the SAME process. I tested this hypothesis by
performing the same analysis on the absolute value of the ERPs: now a
significant positive cluster (p=0.02) emerges at the same latency of
the previous two, and spatially overlapping to their topography.

Do you think that this procedure is plausible, or alternatively that
it is not correct and the effect is just too weak? Anyone faced a
similar problem and has alternative procedures?



Marco Buiatti - Post Doc

Cognitive Neuroimaging Unit  - INSERM U562
Service Hospitalier Frederic Joliot, CEA/DRM/DSV
4 Place du general Leclerc, 91401 Orsay cedex, France
Telephone: +33 1 69 86 77 65    Fax: +33 1 69 86 78 16
E-mail: marco.buiatti at    Web:

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