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# Re: st: st: Handling age in Hazard Ratios

 From Austin Nichols To statalist@hsphsun2.harvard.edu Subject Re: st: st: Handling age in Hazard Ratios Date Mon, 4 Jun 2012 14:12:16 -0400

```Clifton Chow <clifton_chow@post.harvard.edu>:
Where did you get the algebra suggesting that .9299/2*1.0007
represents the turning point?
di ln(.9299)/(2*ln(1.0007))

On Mon, Jun 4, 2012 at 1:46 PM, Clifton Chow
<clifton_chow@post.harvard.edu> wrote:
> I ran a proportional hazards model on the duration of employment and had as my covariates, age and age^2, respectively.  The coefficients and hazard ratios for both variables are below:
>
> Coefficient:  Age     = -.0727
>                  Age^2 = .0007
>
> Hazard Ratio: Age = .9299
>                   Age^2 = 1.0007
>
> I am trying to interpret the diminishing effect of the quadratic term by calculating the age at which the risk changes from a decrease to ian ncrease risk of job loss. I did this by dividing the age coefficient by 2 * age^2 coefficient.  However, when performing this calculation on the raw coefficient, the age of change is 52 (.0727/2*.0007) but in the hazard ratios, that age is 46 (.9299/2*1.0007). Does anyone know which convention to report? I think the difference of 5 years between the two sets of coefficients are important, right?

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