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Thanks for your reply. Are there ways to remedy some of the problems you mentioned?

-Drew
From: MCLAREN, Donald [[log in to unmask]]
Sent: Thursday, December 12, 2013 9:32 PM
To: Sevel,Landrew S
Cc: SPM
Subject: Re: [SPM] Flexible Factorial Warning

I don't think you've made an error - although its possible as you haven't provided your design matrix. The design matrix is not invertible, has no unique solution and thus is badly scaled. 

You should only include subjects that have complete data. While SPM will let you enter incomplete data, no one seems have rigorously tested the impacts missing data. In theory, missing data should not be a problem. However, I wouldn't risk doing something with unknown consequences.

Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Thu, Dec 12, 2013 at 1:08 PM, Sevel,Landrew S <[log in to unmask]> wrote:
Hello all,

I have a flexible factorial design question/concern. I received the following warning when running a model:

Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND =  1.869573e-18. 

The design has subject (N=42), Group (2), session (3), and condition (2) factors

I used the subject option and specified the following conditions per subject
1 1 1
1 2 1
1 3 1
1 1 2
1 2 2 
1 3 2
… For group one and
2 1  1 
2 2 1 
2 3 1
2 1 2
2 2 2
2 3 2
… for group 2

Have I made an error somewhere?

Additionally, am I correct that all subjects need the same amount of data (I.e. I could not include a subject with only 2 sessions)?

Many thanks,

Drew