Hi Doug,

It is indeed correct that columns 1 and 17 are highly correlated. However,

for another version of the fsgd file, where the corresponding class and

covariate values where identical but with other covariates (so leading to

the same columns 1 and 17, other columns are different), all went well.

So probably some other columns are highly correlated as well.

Anyway, what can we do about it? Just leave the offending covariate(s) out?

Cheers,

Message: 1
Date: Thu, 24 Jan 2013 12:51:23 -0500
From: Douglas N Greve <greve@nmr.mgh.harvard.edu>
Subject: Re: [Freesurfer] Problem with glmfit: matrix is
  ill-conditioned
To: freesurfer@nmr.mgh.harvard.edu
Message-ID: <5101749B.4060305@nmr.mgh.harvard.edu>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Hi Ed, the problem is that your covariates are highly correlated. Eg,
column 1 is nearly identical to column 17.
doug

On 01/24/2013 06:36 AM, Ed Gronenschild wrote:
Hi,

Running mri_glmfit ( v5.0.0, Mac OSX10.6) I got he following
error message:

ERROR: matrix is ill-conditioned or badly scaled, condno = 1e+08
Possible problem with experimental design:
Check for duplicate entries and/or lack of range of
continuous variables within a class.
If you seek help with this problem, make sure to send:
  1. Your command line:
  mri_glmfit --y lh.sib_con_cann_aangepast3.thickness.sm0.mgh --fsgd
../../STATS/FSGD/age_gender_scan_educ_hand_cannabis/fsgd_sib_con_cann_aangepast3.fsgd
dods --glmdir lh.sib_con_cann_aangepast3.dods.sm0.glmdir --surf
fsaverage lh --C
../../STATS/FSGD/age_gender_scan_educ_hand_cannabis/group_thickness_gender_scan_age_educ_hand_cann.mtx

  2. The FSGD file (if using one)
  3. And the design matrix above

Please find attached the requested files.

I noticed that rows 68 and 147 of the matrix Xg.dat are identical,
and most probably caused the error.
In the fsgd file I see that the correspondig cases indeed have
identical values, although they are referring to different data.
How to proceed?

Cheers,
Ed