Hi Satra, List,
I think it would be mathematically impossible to estimate the regression coefficients (Betas) for your Data Y (solving B= (X'X)^-1 x X'Y ) for a design matrix X containing 3 identical regressors, i.e. in your case 2 regressors with a constant value for the 'empty' condition, plus the intercept. They are perfectly co-linear (=wrong!). So you will have to find another way to setup your GLM.
Cheers,
Bas
-----Oorspronkelijk bericht-----
Van: SPM (Statistical Parametric Mapping)
[mailto:[log in to unmask]]Namens Stephen J. Fromm
Verzonden: woensdag 23 maart 2005 1:40
Aan: [log in to unmask]
Onderwerp: Re: [SPM] empty conditions in design
On Tue, 22 Mar 2005 16:50:12 -0500, Satrajit Ghosh
<[log in to unmask]> wrote:
>Dear SPMusers,
>
>I have a study in which conditions are not balanced across runs.
>Therefore, run1 may have conditions 1 and 4 and run2 may have
>conditions 2 and 3. SPM complains if I set the onsets for a condition
>to be empty. All it should translate to is an empty column in the
>design matrix, which would be eliminated when the matrix is reduced.
>The reason for entering empty conditions is that I would like to say
>each run has all the conditions, but only enter events for the
>conditions that actually exist in the run.
>
>Is this something that's part of the design intentions? Or am I doing
>something incorrectly?
As far as I can tell, SPM (SPM2 in my case) doesn't let one create empty
columns.
>
>Thanks,
>
>Satra
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