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

 From Yuval Arbel To statalist@hsphsun2.harvard.edu Subject Re: st: Test for significance of the difference between knee locations? Date Thu, 18 Oct 2012 22:42:22 +0200

```You can run the following model:

Cost=beta0xleft+beta1xAgexleft+beta2xAge_sqxleft+gamma0xRight+gamma1xAgexRight+gamma2xAge_sqxRight+u

where Cost is the medical cost, Right (Left) equals 1 for the right
(left) knee and 0 for the left (right) knee, and Age is the patient's
age.

You now need to test beta0=gamma0, beta1=gamma1 and beta2=gamma2 by
the -test- command

On Thu, Oct 18, 2012 at 10:25 PM, Jordan Silberman
<silberman.stata@gmail.com> 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