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Re: st: troubleshooting code for simulating survival data


From   Svend Juul <SJ@SOCI.AU.DK>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: troubleshooting code for simulating survival data
Date   Thu, 29 May 2008 13:42:35 +0200

Michael McCulloch wrote:

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

==============================================================

It seems that contents of the local macro `X' is not defined within 
the program.  That may explain why the code works when not in a 
program, but not in this program.

To examine such problems try:

    set tracedepth 1
    set trace on

Other advice: Tell which command in the program that gave rise to 
the error message, by copying and pasting both command and response 
to you mai..


Hope this helps
Svend

__________________________________________

Svend Juul
Institut for Folkesundhed, Afdeling for Epidemiologi
(Institute of Public Health, Department of Epidemiology)
Vennelyst Boulevard 6
DK-8000  Aarhus C, Denmark
Phone:  +45 8942 6090
Home:   +45 8693 7796
Email:  sj@soci.au.dk
__________________________________________ 


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