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From | Babak Oskooei <babak_cho@yahoo.com> |
To | statalist@hsphsun2.harvard.edu |
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 <ender97@gmail.com> wrote: > From: Philip Ender <ender97@gmail.com> > Subject: Re: st: Potential bug in Stata 11 > To: statalist@hsphsun2.harvard.edu > Date: Wednesday, May 19, 2010, 11:53 AM > Babak Oskooei <babak_cho@yahoo.com> > 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 > * http://www.ats.ucla.edu/stat/stata/ > * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/