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st: st: Handling age in Hazard Ratios


From   "Clifton Chow" <clifton_chow@post.harvard.edu>
To   statalist@hsphsun2.harvard.edu
Subject   st: st: Handling age in Hazard Ratios
Date   Mon, 04 Jun 2012 13:24:12 -0500

I got it from Wooldridge, p. 193.  It's just the maximum.


>  -------Original Message-------

Where did you get the algebra suggesting that .9299/2*1.0007 represents the turning point?
 di ln(.9299)/(2*ln(1.0007))

>  From: Clifton Chow <clifton_chow@post.harvard.edu>
>  To: statalist@hsphsun2.harvard.edu
>  Subject: st: Handling age in Hazard Ratios
>  Sent: 04 Jun '12 12:46
>  
>  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?
>  
>  Thanks
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