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st: troubleshooting code for simulating survival data


From   Michael McCulloch <mm@pinest.org>
To   Statalist <statalist@hsphsun2.harvard.edu>
Subject   st: troubleshooting code for simulating survival data
Date   Wed, 28 May 2008 11:51:19 -0700

Hello,
I've written the following do-file to simulate survival data, in the case of exponential distribution with one treatment variable (a) and no covariates. The code works when not in a program, and returns the specified Beta-coefficient (-0.8). May I ask for help in fine-tuning the program? I'm getting error message: " 'r(a)' evaluated to missing in full sample".

clear
capture program drop sim_surv
program define sim_surv, rclass
tempname lambda a id t
set obs 10 //create 10 observations
gen `id'=_n //Create ID numbers
set seed 1235 //set random number seed for reproducibility
gen `a'=0 + int(2*uniform()) //Generate treatment: discrete 0/1 uniform random variables
gen `lambda'=-2
gen `t'=(ln(uniform())/(`lambda'*exp(-0.8*`a'))) // using Bender, 2005
stset `t'
stcox `t'
indeplist, local
foreach var of varlist `X' {
return scalar `var' = exp(_b[`var'])
}

end
set seed 12358
bootstrap a=r(a), eform reps(10): sim_surv
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