Re: [Freesurfer] testing a quadratic effect of age

yes, that works too

On 02/24/2014 11:20 AM, Yang, Daniel wrote:

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.edu mailto: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
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