Hi Doug,

Thanks for the response.  I have had a read about demeaning on the forum. I had a couple of questions:

1) If I want to include age as well as ICV as nuisance variables in a DODS analysis comparing thickness between patients and controls, should I demean (+ ? normalise) the age as well as the ICV.

2) Why the need to normalise as well as demean the ICV - I hadn't come across this in the forums.

Thanks.

Mahinda




On Mon, Feb 27, 2012 at 3:12 PM, Douglas N Greve <greve@nmr.mgh.harvard.edu> wrote:
Hi Mahinda, try demeaning and normalizing the ICV values (ie, subtract the mean and divide by the stddev).
doug

Mahinda Yogarajah wrote:
Dear Experts,

I am trying to carry out a simple 2 group (conrol and patient) analysis with ICV as nuisance factor, and thickness as the dependent variable.

However whenever I include ICV (inputed by following the qdec tutorial and the generate stats table) I get the following output and error message:
------------------------------------------------------------------

lh-Avg-Intercept-thickness -----------------------

Does the average thickness differ from zero?

 1.000   1.000   0.000   0.000;



lh-Avg-thickness-IntraCranialVol-Cor -----------------------

Does the correlation between thickness and IntraCranialVol, accounting for diagnosis, differ from zero?

 0.000   0.000   1.000   1.000;



lh-Diff-Patients-Control-Intercept-thickness -----------------------

Does the average thickness differ between Patients and Control?

 1.000  -1.000   0.000   0.000;



lh-Diff-Patients-Control-Cor-thickness-IntraCranialVol -----------------------

Does the thickness--IntraCranialVol correlation differ between Patients and Control?

 0.000   0.000   1.000  -1.000;



ninputs = 40

Checking inputs

nframestot = 40

Allocing output

Done allocing

nframes = 40

Writing to /home/myogaraj/freesurfer/qdec/Untitled/y.mgh

gdfReadHeader: reading /home/myogaraj/freesurfer/qdec/Untitled/qdec.fsgd

INFO: DeMeanFlag keyword not found, DeMeaning will NOT be done.

Continuous Variable Means (all subjects)

0 IntraCranialVol 1.42401e+06 259214

Class Means of each Continuous Variable

1 diagnosisPatients 1343236.0559

2 diagnosisControl 1497089.0952

INFO: gd2mtx_method is dods

Reading source surface /home/myogaraj/freesurfer/fsaverage/surf/lh.white

Number of vertices 163842

Number of faces    327680

Total area         65416.648438

AvgVtxArea       0.399267

AvgVtxDist       0.721953

StdVtxDist       0.195470



$Id: mri_glmfit.c,v 1.196.2.6 2011/05/05 20:54:25 greve Exp $

cwd /home/myogaraj/freesurfer/qdec

cmdline mri_glmfit --y /home/myogaraj/freesurfer/qdec/Untitled/y.mgh --fsgd /home/myogaraj/freesurfer/qdec/Untitled/qdec.fsgd dods --glmdir /home/myogaraj/freesurfer/qdec/Untitled --surf fsaverage lh --label /home/myogaraj/freesurfer/fsaverage/label/lh.aparc.label --C /home/myogaraj/freesurfer/qdec/Untitled/contrasts/lh-Avg-Intercept-thickness.mat --C /home/myogaraj/freesurfer/qdec/Untitled/contrasts/lh-Avg-thickness-IntraCranialVol-Cor.mat --C /home/myogaraj/freesurfer/qdec/Untitled/contrasts/lh-Diff-Patients-Control-Intercept-thickness.mat --C /home/myogaraj/freesurfer/qdec/Untitled/contrasts/lh-Diff-Patients-Control-Cor-thickness-IntraCranialVol.mat

sysname  Linux

hostname localhost.localdomain

machine  x86_64

user     myogaraj

FixVertexAreaFlag = 1

UseMaskWithSmoothing     1

OneSampleGroupMean 0

y    /home/myogaraj/freesurfer/qdec/Untitled/y.mgh

logyflag 0

usedti  0

FSGD /home/myogaraj/freesurfer/qdec/Untitled/qdec.fsgd

labelmask  /home/myogaraj/freesurfer/fsaverage/label/lh.aparc.label

maskinv 0

glmdir /home/myogaraj/freesurfer/qdec/Untitled

IllCondOK 0

ReScaleX 1

DoFFx 0

Creating output directory /home/myogaraj/freesurfer/qdec/Untitled

Loading y from /home/myogaraj/freesurfer/qdec/Untitled/y.mgh

INFO: gd2mtx_method is dods

Saving design matrix to /home/myogaraj/freesurfer/qdec/Untitled/Xg.dat

Normalized matrix condition is 175.031

Matrix condition is 1e+08

Found 148151 points in label.

Pruning voxels by thr: 0.000000

Found 148025 voxels in mask

Saving mask to /home/myogaraj/freesurfer/qdec/Untitled/mask.mgh

Reshaping mriglm->mask...

search space = 73649.347769

DOF = 36

Starting fit and test

Fit completed in 0.0710833 minutes

Computing spatial AR1 on surface

Residual: ar1mn=0.995672, ar1std=0.001628, gstd=6.144582, fwhm=14.469384

Writing results

 lh-Avg-Intercept-thickness

   maxvox sig=19.391  F=349.349  at  index 102911 0 0    seed=1330322022

 lh-Avg-thickness-IntraCranialVol-Cor

   maxvox sig=-3.43147  F=15.4402  at  index 109705 0 0    seed=1330322022

 lh-Diff-Patients-Control-Intercept-thickness

   maxvox sig=3.99329  F=19.0823  at  index 28994 0 0    seed=1330322022

 lh-Diff-Patients-Control-Cor-thickness-IntraCranialVol

   maxvox sig=-3.79353  F=17.7548  at  index 129172 0 0    seed=1330322022

mri_glmfit done

ninputs = 4

Checking inputs

nframestot = 4

Allocing output

Done allocing

nframes = 4

Writing to /home/myogaraj/freesurfer/qdec/Untitled/contrasts.sig.mgh

reading colortable from annotation file...

colortable with 36 entries read (originally /autofs/space/terrier_001/users/nicks/freesurfer/average/colortable_desikan_killiany.txt)

reading colortable from annotation file...

colortable with 36 entries read (originally /autofs/space/terrier_001/users/nicks/freesurfer/average/colortable_desikan_killiany.txt)

gdfReadHeader: reading /home/myogaraj/freesurfer/qdec/Untitled/y.fsgd

INFO: ignoring tag Creator

INFO: ignoring tag SUBJECTS_DIR

INFO: ignoring tag SynthSeed

INFO: NOT demeaning continuous variables

Continuous Variable Means (all subjects)

0 IntraCranialVol 1.42401e+06 259213

Class Means of each Continuous Variable

1 diagnosisPatients 1343236.3158

2 diagnosisControl 1497089.0476

MatrixMultiply: m1 is null!


No such file or directory

---------------------------------------------------------

Can anyone advise ?

Thanks.

Mahinda


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