Sorry Brad, my mistake - you actually only need one extra EV to
extend the main part of the design from tripled to quadrupled:
1 1 1 1 0 0
1 1 1 0 1 0
1 1 1 0 0 1
-1 0 0 1 0 0
-1 0 0 0 1 0
-1 0 0 0 0 1
0 -1 0 1 0 0
0 -1 0 0 1 0
0 -1 0 0 0 1
0 0 -1 1 0 0
0 0 -1 0 1 0
0 0 -1 0 0 1
and to work out the contrasts:
A = a + b + c
B = -a
C = -b
D = -c
A-B = 2a + b + c = [2 1 1]
A-C = a + 2b + c = [1 2 1]
A-D = a + b + 2c = [1 1 2]
B-C = -a + b = [-1 1 0]
B-D = -a + c = [-1 0 1]
C-D = -b + c = [0 -1 1]
etc.
This should work hopefully.
Cheers, Steve.
On 20 Oct 2006, at 20:34, Brad Goodyear wrote:
>
> Hi Steve.
>
> I have tried extending the triple t-test example to do a quadruple
> one.
> I get a linear combination warning at the design stage, and a
> singular matrix error upon running.
>
> Attached is the design file?
> Would you be able to take a quick peek?
>
> Thanks,
>
> BRad
>
> <design.fsf>
>
>
------------------------------------------------------------------------
---
Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
------------------------------------------------------------------------
---
|