Dear Chunhong,
[log in to unmask] wrote:
> Dear Will,
>
> Thanks so much for your patience and time! I'll read them carefully. Could you
> please see below for quick questions? Thanks!
>
>
>> The overall test [1 -1 0; 0 1 -1] tests for a difference between the
>> first and second levels OR a difference between the 2nd and 3rd levels
>> OR any linear combination thereof.
>
> So, here I thought I should use [1 -1 0; 0 1 -1; 1 0 -1] as I also want to see
> the difference between the first and third levels. Why it is [1 -1 0; 0 1 -1]
> instead of [1 -1 0; 0 1 -1; 1 0 -1]? Thanks!
>
Because if you add the first row to the second you get the third row.
Another way of saying this is that the third row is a linear combination
of the first two.
So, the two contrasts are testing for the same thing (you could use either).
> If for some reason, the amount of subjects is not exactly the same in task C (10
> subjects)as that in task A and B (12subjects), could I still use the same
> methods which you suggested before (full factorial)?
yes.
Best,
Will.
Thanks!
>
>
> Best wishes,
> Chunhong
>
>
>
--
William D. Penny
Wellcome Trust Centre for Neuroimaging
University College London
12 Queen Square
London WC1N 3BG
Tel: 020 7833 7475
FAX: 020 7813 1420
Email: [log in to unmask]
URL: http://www.fil.ion.ucl.ac.uk/~wpenny/
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