Dear Doug,
Would you please shine some light on what quantities are being plotted in those statistical maps of QDEC? Some linear combination of the columns of the design matrix?
Also, what is the "default" design matrix?
Thank you very much!
Sincerely, Ye
On Tue, Aug 13, 2013 at 11:45 PM, Douglas Greve greve@nmr.mgh.harvard.eduwrote:
1 and 3 are the same model. Calling a variable a nuisance factor is just a description. The model is actually y = age*meditation*b1 + meditation*b2 + err = y_hat + err
doug
On 8/13/13 6:12 PM, ye tian wrote:
Dear Freesurfers,
I am studying cortical thickness as a function of age (continuous) and meditation practice (categorical, level1=Normal, level2=TM). I have three separate cases of qdec, regression1, regression2 and regression3.
Regression1: Discrete (Fixed Factor) = meditation; Continuous (Covariate) = age Regression2: Discrete (Fixed Factor) = meditation; Regression3: Discrete (Fixed Factor) = meditation; Nuisance Factor = age
For the question "Does the average thickness differ between Normal and TM?", Regression1 and Regression3 have identical result, which is different from Regression2, i.e., (1 = 3 !=2 ). May I infer from this result the following about qdec:
- Regression1 and Regression3 both fit cortical thickness,y, to the
model y = b0 + age*b1 + meditation*b2 + err = y_hat + err Regression2 fits: y = b0 + b2*meditation + err = y_hat + err
- Some function of y_hat goes into the "average thickness", hence the
difference between 2 and the others.
However, what role does "Nuisance Factor" play in this case?
Thank you very much!
Sincerely, Ye
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