depsamplesF

Stephan Moratti moratti at MED.UCM.ES
Wed Sep 9 13:57:44 CEST 2009


Hi Eric y Nadia,

Ok, I have made a test of depsamplesF comparing results of depsamplesF and 
SPSS. I get the same results. I used data from an experiment and chose a 
timepoint and one channel that were indicated to be significant by 
dempsamplesF. In the attached TEST_dempsamplesF.mat file it is "testmat" 
(24 subjects 3 conditions). The variable "dat" is the reshaped "testmat". The 
structure "s" contains the results of depsamplesF. I added the variable 
scaledstat as the field "F" to "s" as it is the F value. The attached 
file "SPSSoutput.bmg" is a screen shot of the SPSS output entering testmat in 
a MANOVA. The results  are the same:
F(2, 22) = 6.627, p = 0.006

We can also calculate Wilk's lambda from T^2 (see page 232 formula 5-13 of 
the Johnson 1998 edition) as:

lambda = 1/(1 + s.stat/(24-1));

and get 0.624, the same as in SPSS. Maybe, as people are more used to F 
values, it would be useful to have the F(scaledstat)  value also in the "s" 
structure (and later after using timelockstats or freqstats to have a matrix 
containing the F values besides the T^2 values).

Thanks for implementing that great stuff in fieldtrip and making it accessible 
for all users !

Best,

Stephan


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