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st: Using Aalen's additive hazard model in Stata

From   Anwar Musah <[email protected]>
To   "[email protected]" <[email protected]>
Subject   st: Using Aalen's additive hazard model in Stata
Date   Wed, 23 Apr 2014 14:09:41 +0100

Dear Statalist,

I have an outcome which is a right censored variable coded as 1 for those who developed cancer and 0 otherwise. The main predictor variable is the individual's exposure level to an environmental contaminant which is categorised using quintiles and labelled as follows: 1 (<=10.8 mg/kg), 2 (10.9 - 14.2 mg/kg), 3 (14.3 - 17.3 mg/kg), 4 (17.4 - 21.4 mg/kg) and 5 (>=21.5 mg/kg).

Initially, I fitted a Cox's proportional-hazards model to estimate the risk of developing cancer according to these exposure categories; however, there is violation of the proportional-hazards assumption due the time-dependent effects the exposure might have on the cancer outcome. My question - is it plausible to use the Aalen's model as an alternative to generate cumulative hazard coefficients for each of the last four categories of my exposure variable with the first category being the referent group? 

"xi: stlh i.arsenic_cat, level(95) nograph"

Above syntax seems to work, however I am unsure of this methodology - most examples seem to focus on predictor variables that are only binary.

Thank you,
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