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Re: st: Test for significance of the difference between knee locations?


From   Yuval Arbel <yuval.arbel@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Test for significance of the difference between knee locations?
Date   Thu, 18 Oct 2012 22:45:45 +0200

I forgot to mention that Age_sq is AgexAge

If i'm not mistaken Jordan is from the medical field

On Thu, Oct 18, 2012 at 10:36 PM, Roger B. Newson
<r.newson@imperial.ac.uk> wrote:
> What is the "knee" of a quadratic model? I never knew that they had knees
> (although I might expect a 3-parameter linear spline to have a knee).
>
> Best wishes
>
> Roger
>
> Roger B Newson BSc MSc DPhil
> Lecturer in Medical Statistics
> Respiratory Epidemiology and Public Health Group
> National Heart and Lung Institute
> Imperial College London
> Royal Brompton Campus
> Room 33, Emmanuel Kaye Building
> 1B Manresa Road
> London SW3 6LR
> UNITED KINGDOM
> Tel: +44 (0)20 7352 8121 ext 3381
> Fax: +44 (0)20 7351 8322
> Email: r.newson@imperial.ac.uk
> Web page: http://www.imperial.ac.uk/nhli/r.newson/
> Departmental Web page:
> http://www1.imperial.ac.uk/medicine/about/divisions/nhli/respiration/popgenetics/reph/
>
> Opinions expressed are those of the author, not of the institution.
>
>
> On 18/10/2012 21:25, Jordan Silberman wrote:
>>
>> Hi Stata folks,
>>
>> I'm searching for a method I can run in Stata that will allow me to
>> test whether the location of the knee for one quadratic model
>> significantly differs from that of another quadratic model.
>>
>> I have 2 quadratic models, each modeling a different category of
>> healthcare costs as a function of age. Let's say, for illustrative
>> purposes, that the knee of the first quadratic model occurs at age 45,
>> and the knee for the second model occurs at age 55.
>>
>> Can anybody suggest a method for testing whether the former "knee age"
>> differs significantly from the latter "knee age?" The idea is to test
>> the hypothesis that there is a difference across the 2 models in the
>> age at which the costs growth rate begins to increase.
>>
>> Any suggestions would be greatly appreciated.
>>
>> Thanks,
>> Jordan
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-- 
Dr. Yuval Arbel
School of Business
Carmel Academic Center
4 Shaar Palmer Street,
Haifa 33031, Israel
e-mail1: yuval.arbel@carmel.ac.il
e-mail2: yuval.arbel@gmail.com
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