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Re: st: RE: Growth curve with -gllamm- (any way to get peak velocityand height?)


From   Joseph Wagner <joseph.wagner@wright.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: Growth curve with -gllamm- (any way to get peak velocityand height?)
Date   Fri, 10 Aug 2007 12:53:59 -0400

1. We want to fit the individuals together.
2. In terms of functional forms, by including a quadratic term our simple model (using a measurement, age, and the square of age fits well.


Nick Cox wrote:

This fills in some of the background science.
It seems to leave unclear:
1. Quite how demographic data are to be related to individuals. More broadly, whether you intend fitting
individuals separately or together. My guess is the latter, but it helps to spell things out.
2. Whether you have specific discipline-approved growth curve functional forms in mind or are going
to use more general methods.
Even if you answer these questions, I will not be able to add very much more, if anything, but others might start tuning in and give you specific advice.
Nick n.j.cox@durham.ac.uk
Joseph Wagner

The research involves craniofacial skeletal growth measurements. The data consist of several angle measurements at junctions between bones and length measurements of specific areas of bone. We have demographic data as well. We get measurements (using x-rays) from individuals annually over their lifetime. We want to know at which point the greatest rate of growth occurs and the peak growth velocity for individuals and the mean for our entire sample. We also want to know the rate of bone recession in older persons.

Nick Cox wrote:

It isn't obvious from this information alone that -gllamm-
is the only or even the best way to do it. That said, there will be ways to get key properties of fitted growth curves, even if only numerically. Quite how will depend on what you do precisely, so better answers
might depend on further information.
Nick n.j.cox@durham.ac.uk
Joseph Wagner

I have data composed of yearly jaw xray measurements over a 20 year
period. I wish to do some growth curve analyses of these data so I plan
to use -gllamm- but I was wondering, is there a way to get the mean peak
velocity and the mean peak height of the growth curve?
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--
Joseph H. Wagner, M.P.H.
Lifespan Health Research Center
Wright State University Boonshoft School of Medicine
3171 Research Blvd.
Kettering, OH 45420-4014

(937) 775-1494 (LHRC office)
(937) 775-1456 (fax)

joseph.wagner@wright.edu

Visit the Lifespan Health Research Center Home Page at:
http://www.med.wright.edu/lhrc
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