Let's say you have four groups with 10 20 30 40 (100 total). The first
group would get a weight of .25 where it only had 10% of the total. I
don't think there is any way around this.
On 2/18/14 4:07 PM, Yang, Daniel wrote:
Doug, sorry, I am not sure I can fully understand.
Do you mean the results are weighted MORE toward groups with smaller
sample sizes (than groups with larger sample sizes)?
--
Daniel (Yung-Jui) Yang, Ph.D.
Postdoctoral Researcher
Yale Child Study Center
New Haven, CT
Tel: (203) 737-5454
E-mail: _yung-jui.yang@yale.edu_
On 2/18/14 2:13 PM, "Douglas N Greve" <gr...@nmr.mgh.harvard.edu
<mailto:gr...@nmr.mgh.harvard.edu>> wrote:
It will tend to weight smaller groups by a proportion greater
than the
number of subjects in the group.
On 02/18/2014 01:58 PM, Yang, Daniel wrote:
Thanks Doug! One follow-up question: since it's [0.25 0.25 0.25
0.25], would the effect be biased toward large sample sizes
in one of
the groups (versus the other groups)?
Or, does FreeSurfer qdec take care of the unequal cell, in a
possible
way analogous to using Type III SS in the traditional ANOVA?
Best,
Daniel
--
Daniel (Yung-Jui) Yang, Ph.D.
Postdoctoral Researcher
Yale Child Study Center
New Haven, CT
Tel: (203) 737-5454
E-mail: _yung-jui.yang@yale.edu_ <mailto:_yung-jui.yang@yale.edu_>
On 2/18/14 1:30 PM, "Douglas N Greve"
<gr...@nmr.mgh.harvard.edu <mailto:gr...@nmr.mgh.harvard.edu>
<mailto:gr...@nmr.mgh.harvard.edu>
<mailto:gr...@nmr.mgh.harvard.edu%3E>> wrote:
That looks right to me
doug
On 02/18/2014 10:08 AM, Yang, Daniel wrote:
Dear FreeSurfer experts,
I have two binary factors (F1: F1L1 F1L2; F2: F2L1
F2L2), 1
covariate
(COV), and 1 nuisance factor (NUI). I want to make
sense of some
specification of the regressors and contrasts.
Because they are not described
in
http://surfer.nmr.mgh.harvard.edu/fswiki/Fsgdf4G1V, I post my
understanding below. Can you let me know if it is
correct?
This model using the DODS method will have 12 regressors:
Regressor1: 1's for F1L1 F2L1, 0 otherwise (i.e.,
offset for
Group 1)
Regressor2: 1's for F1L1 F2L2, 0 otherwise (i.e,
offset for
Group 2)
Regressor3: 1's for F1L2 F2L1, 0 otherwise (i.e.,
offset for
Group 3)
Regressor4: 1's for F1L2 F2L2, 0 otherwise (i.e.,
offset for
Group 4)
Regressor5: COV for Group1 subjects, 0 otherwise
(i.e., COV
slope for
Group 1)
Regressor6: COV for Group2 subjects, 0 otherwise
(i.e., COV
slope for
Group 2)
Regressor7: COV for Group3 subjects, 0 otherwise
(i.e., COV
slope for
Group 3)
Regressor8: COV for Group4 subjects, 0 otherwise
(i.e., COV
slope for
Group 4)
Regressor9: NUI for Group1 subjects, 0 otherwise
(i.e., NUI
slope for
Group 1)
Regressor10: NUI for Group2 subjects, 0 otherwise
(i.e., NUI
slope for
Group 2)
Regressor11: NUI for Group3 subjects, 0 otherwise
(i.e., NUI
slope for
Group 3)
Regressor12: NUI for Group4 subjects, 0 otherwise
(i.e., NUI
slope for
Group 4)
Description1: Does the correlation between thickness
and COV,
accounting for F1 and F2, differ from 0? Nuisance
factors: NUI
Contrast1:
[0 0 0 0 0.25 0.25 0.25 0.25 0 0 0 0]
Best,
Daniel
--
Daniel (Yung-Jui) Yang, Ph.D.
Postdoctoral Researcher
Yale Child Study Center
New Haven, CT
Tel: (203) 737-5454
E-mail: _yung-jui.yang@yale.edu_
<mailto:_yung-jui.yang@yale.edu_>
<mailto:_yung-jui.yang@yale.edu_>
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--
Douglas N. Greve, Ph.D.
MGH-NMR Center
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Douglas N. Greve, Ph.D.
MGH-NMR Center
gr...@nmr.mgh.harvard.edu <mailto:gr...@nmr.mgh.harvard.edu>
Phone Number: 617-724-2358
Fax: 617-726-7422
Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting
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