Thanks, Doug. I will standardize the age first.
I can also think of another way of doing this: divide the sample into 4 age bins and treat age as a Discrete Factor with 4 levels.
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
On 2/24/14 11:10 AM, "Douglas N Greve" <greve@nmr.mgh.harvard.edumailto:greve@nmr.mgh.harvard.edu> wrote:
Yes, though you might want to demean age before computing the quadratic. doug
On 02/24/2014 10:13 AM, Yang, Daniel wrote: Hi FreeSurfer Experts,
With age as a continuous variable, qdec can test the linear effect of age. To test the quadratic effect of age, do I just create a curvilinear term like age*age and add into the existing equation?
For example:
original equation: Y = intercept + age + Factor + age*Factor
new equation: Y = intercept + age + Factor + age*Factor + age*age + age*age*Factor
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_
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-- Douglas N. Greve, Ph.D. MGH-NMR Center greve@nmr.mgh.harvard.edumailto:greve@nmr.mgh.harvard.edu Phone Number: 617-724-2358 Fax: 617-726-7422
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