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RE: st: Power estimation in Cox ph model

From   "ZHIVIN Sergey" <>
To   <>
Subject   RE: st: Power estimation in Cox ph model
Date   Wed, 29 Feb 2012 15:17:36 +0100

Dear Steve and all Statalist,

Good to know about Stata name, I always wrote in capitals taking in mind the examples of SAS and SPSS...Sorry!

I have read a manual on -stpower-, but I still have questions. Could you help me please?
As I wrote our study is historical cohort, and now I want to estimate power of Cox model between exposure to hydrazine and lung cancer risk. So, we have 53 deaths in 2387 workers (however, not all workers are exposed).  I obtained sd of log for cumulative exposure to hydrazine, and failprob=53 deaths/2387 workers. HR is set to 1.20...
Does my formula look correct?

stpower cox, failprob(), sd() n(2387) hratio (1.20)

Or should I take not all workers as n?
I also found the models with stpower cox 1. Should I use it instead? What is the meaning of 1 (is it just ln of HR)?

Thank you!

-----Message d'origine-----
De : [] De la part de Steve Samuels
Envoyé : mardi 28 février 2012 23:48
À :
Objet : Re: st: Power estimation in Cox ph model

Welcome to Statalist, Sergey!

See the entry for -stpower- in the Stata Survival manual.

By the way, the correct spelling of our favorite program is "Stata", not "STATA".  In English, words all capitalized are "acronyms", meaning that their letters stood for words in the original, sometimes abandoned, names.  So, for example, "SAS" and "SPSS" are acronyms, because their original names were "Statistical Analysis System" and "Statistical Package for the Social Sciences".  

"Stata" is a name the company made up and its letters don't stand for anything else (see the end of the Statalist FAQ), so the only capitalized letter is the initial "S", just as in our names.


On Feb 28, 2012, at 5:44 AM, ZHIVIN Sergey wrote:

 we want to do several models ( 1-univariate model with number of death from cancer and exposure to different chemicals, 2-the previous model adjusted for exposure to internal radiation).
I have done a literature review and now I know hazard ratios of such exposures in previous studies. The problem I don't know how to construct my STATA formula for power. Could you help me with this? Number of deaths and study sample are known.

Have a good day,
Sergey Zhivin    

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