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Re: st: Potential bug in Stata 11
From
Babak Oskooei <[email protected]>
To
[email protected]
Subject
Re: st: Potential bug in Stata 11
Date
Wed, 19 May 2010 09:11:59 -0700 (PDT)
Thanks Phil for attending to my question/problem. I commented out the same, what it might look, redundant code and it works fine.
However, if I change the covariate effect, i.e. 4.159, to 2.079 it works fine without even commenting that piece of code out. Here is the code and Stata 11 output:
********** Code
clear all
set mem 200m
set obs 10000
set seed 30101
gen x = uniform()
gen y = invnorm(uniform())
gen eta=y*2.079
gen u=-ln(1-uniform())/0.02 /* exp dist with given hazard */
gen t=exp(-eta)*u
gen d=1
noi{
stset t, failure(d)
stcox y, nohr
}
************** Output
. stset t, failure(d)
failure event: d != 0 & d < .
obs. time interval: (0, t]
exit on or before: failure
------------------------------------------------------------------------------
10000 total obs.
0 exclusions
------------------------------------------------------------------------------
10000 obs. remaining, representing
10000 failures in single record/single failure data
8371043 total analysis time at risk, at risk from t = 0
earliest observed entry t = 0
last observed exit t = 3401842
. stcox y, nohr
failure _d: d
analysis time _t: t
Iteration 0: log likelihood = -82108.928
Iteration 1: log likelihood = -75222.589
Iteration 2: log likelihood = -74737.776
Iteration 3: log likelihood = -74734.026
Iteration 4: log likelihood = -74734.026
Refining estimates:
Iteration 0: log likelihood = -74734.026
Cox regression -- no ties
No. of subjects = 10000 Number of obs = 10000
No. of failures = 10000
Time at risk = 8371043.106
LR chi2(1) = 14749.80
Log likelihood = -74734.026 Prob > chi2 = 0.0000
------------------------------------------------------------------------------
_t | Coef. Std. Err. z P>|z| [95% Conf. Interval]
-------------+----------------------------------------------------------------
y | 2.087067 .0193951 107.61 0.000 2.049053 2.12508
------------------------------------------------------------------------------
. }
********************************************************
This was part of a larger code in which I will use the X variable that was commeneted out by Phil.
In my opinion, something is not right.
Babak
--- On Wed, 5/19/10, Philip Ender <[email protected]> wrote:
> From: Philip Ender <[email protected]>
> Subject: Re: st: Potential bug in Stata 11
> To: [email protected]
> Date: Wednesday, May 19, 2010, 11:53 AM
> Babak Oskooei <[email protected]>
> wrote:
>
> I have been conducting some simulations in Stata and faced
> a
> computational problem in Stata 11. I run the same code in
> Stata 9 and
> it gives me the right answer. I would be grateful for any
> feedback on
> this. Below, I include the code and the output from both
> version 9 and
> version 11. I am simply simulating conditional
> time-to-event data that
> are exponentially distributed with one normally
> distributed
> covariate. ....
> --------
>
> Using Stata 11 running on Mac OX 10.6.3, I commented out
> the line that
> generates x like this:
>
> *gen x = uniform()
>
> The code ran fine with these results:
>
> Iteration 0: log likelihood = -82108.928
> Iteration 1: log likelihood = -71818.568
> Iteration 2: log likelihood = -69286.528
> Iteration 3: log likelihood =
> -69035.66
> Iteration 4: log likelihood = -69032.801
> Iteration 5: log likelihood = -69032.627
> Refining estimates:
> Iteration 0: log likelihood = -69032.613
> Iteration 1: log likelihood = -69032.613
>
> Cox regression -- no ties
>
> No. of subjects = 10000
>
> Number of obs =
> 10000
> No. of failures = 10000
> Time at risk = 1679070425
>
>
>
> LR chi2(1) =
> 26152.63
> Log likelihood = -69032.613
>
> Prob > chi2
> = 0.0000
>
> ------------------------------------------------------------------------------
> _t |
> Coef. Std. Err. z
> P>|z| [95% Conf.
> Interval]
> -------------+----------------------------------------------------------------
> y
> | 4.177157 .0343322 121.67 0.000
> 4.109867 4.244447
> ------------------------------------------------------------------------------
>
> If the lise is not commented out then I get the same error
> message as Babak.
>
> --
> Phil Ender
> UCLA Statistical Consulting Group
> *
> * For searches and help try:
> * http://www.stata.com/help.cgi?search
> * http://www.stata.com/support/statalist/faq
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>
*
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