We are analyzing some PET data with SPM, and I am looking for an explanation of
what the plots of the SPM statistics mean.  It is easy to get an intuitive sense of
what is being plotted, but is there any documentation anywhere describing the
plots, both the 'size of effects' plots and the 'fitted and adjusted responses'
plots, explaining exactly what the quantities are which are plotted (what are the
'responses'?), what units if any they have etc.

We are using SPM99b.  On the Cambridge MRC-CBU website, there is a brief
explanation of plots for SPM96, including ..... "Pressing "conditions" in the lower
left-hand window will produce a histogram with each x-axis number being a
condition, and the size of the bar (y-axis) being the blood flow for the peak
chosen."  Presumably this would be normalized blood flow. Is SPM99 different in the
units of what is plotted - in the SPM99 manual, it is written that "The plot will
show effect size and error bars (in %)."  Is this talking about the same plots?
effect size as % of what?  how could one use these values to calculate the blood
flow for the peak chosen?  is there a file in which the numerical data which
appears on the plot is available in text format?

Also the plots I have seen are all for one particular voxel, is there a way to get
the average size of effects or responses for a cluster?  even though significant
findings in SPM are often reported at the voxel level, does it make sense to
consider size of effects, say in 2 subject groups at one particular voxel?  it
seems to me that it would be more meaningful to report size of effects for a
slightly wider region like a cluster - as an SPM novice, am I still failing to
understand something here? any comments?

Thanks very much
Nanette
--
Nanette Chana Freedman, Ph.D.
Hadassah University Hospital
Department of Medical Biophysics and Nuclear Medicine
Kiryat Hadassah
P.O.B. 12000
91120 Jerusalem, ISRAEL
Tel:  972 2 6776 720 (work)
Fax: 972 2 6421 203 (work)
Tel: 972 2 5636 174 (home)
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