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st: st: Handling age in Hazard Ratios

From   "Clifton Chow" <>
Subject   st: st: Handling age in Hazard Ratios
Date   Mon, 04 Jun 2012 12:46:00 -0500

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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