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Hi Eva,

Yes - that looks fine. Presumably your  C15 (C mean) should have been  
[0 0 1 0]?
You could also have another contrast [1 1 1 1] to look for a  
significant mean averaged across all groups.

In general f-tests look at the combined explanatory power of a subset  
of specified contrasts. So an f-test could be used, for example, to  
look for significance in any of the groups (like an omnibus test, or a  
test for a main effect of group) by doing an f-test combining  
contrasts C13,14,15,16.

Cheers, Mark.

----
Dr Mark Woolrich
EPSRC Advanced Research Fellow University Research Lecturer

Oxford University Centre for Functional MRI of the Brain (FMRIB),
John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK.

Tel: (+44)1865-222782 Homepage: http://www.fmrib.ox.ac.uk/~woolrich




On 11 Aug 2009, at 12:20, Eva Kenny wrote:

> Hi,
>
> Id like to run higher-level FEAT analysis on 4 subject groups. Is  
> the model
> below correct for investigating differences between groups and group
> averages?
> Also, what would be the advantage of running F-tests also?
>
> Many thanks,
> Eva
>
>
> Number of EVs = 4
>
> Group	EV1	EV2	EV3	EV4
> 1	1	0	0	0
> 1	1	0	0	0
> 2	0	1	0	0
> 2	0	1	0	0
> 3	0	0	1	0
> 3	0	0	1	0
> 4	0	0	0	1
> 4	0	0	0	1
>
> Contrasts = 16 		F-test = 0
> 	Title		EV1	EV2	EV3	EV4
> C1	A>B		1	-1	0	0	
> C2	B>A		-1	1	0	0
> C3	A>C		1	0	-1	0
> C4	C>A		-1	0	1	0
> C5	A>D		1	0	0	-1
> C6	D>A		-1	0	0	1
> C7	B>C		0	1	-1	0
> C8	C>B		0	-1	1	0
> C9	B>D		0	1	0	-1
> C10	D>B		0	-1	0	1
> C11	C>D		0	0	1	-1
> C12	D>C		0	0	-1	1
> C13	A Mean	             1           0           0           0
> C14	B Mean	             0           1           0           0
> C15	C Mean	             1           0           1           0
> C16	D Mean	             0           0           0           1
>