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From |
"Smith, Paul Bradley" <SmithP5@uthscsa.edu> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: bootstrapping -- why am I not getting the full sample size? |

Date |
Fri, 21 Oct 2005 15:32:17 -0500 |

All, I'm trying to bootstrap a cost-effectiveness ratio, using a user-written program. Components are differences in cost of treatment, and differences in survival time. My user-written program works just right, but it bombs when submitted to the bootstrap routine. What happens is that the first resample (after the run on the entire dataset) contains a resample with about a third of the patients that were in the original sample. The truncated sample size exactly corresponds to the number of control group patients in the study. Given that there are no experimental group patients in the control group :-) the estimation of restricted mean survival time for the experimental group naturally bombs out. I've tried several fixes, including reordering the component procedures in the user-written program, applying --stset, clear-- to clear the survival settings for the data, and doing a --sum-- on a variable that has valid observations for all cases just before the end of the program. Nothing seems to get me out of the hole of having a much smaller dataset. Any ideas? I suspect it has something to do with --stset--ing the data, as the routine runs fine if the survival stuff is omitted. Perhaps I'm missing something obvious, though. Thanks, Brad Smith Here's a pared-down version of my user-written program that works with the hmohiv dataset: ------------------------------------------------------------------------ sysuse hmohiv capture program drop myRatio program myRatio, rclass version 9 *compute restricted mean survival times stset time, f(censor=0) stci if drug==0 , rmean local contime = r(rmean) stci if drug==1 , rmean local exptime = r(rmean) *compute ratio local survdif = ((`exptime' - `contime')/365) return scalar ratio = `survdif' end And the bootstrap call (set to 2 since the subsequent runs weren't working): bootstrap ratio=r(ratio), noisily reps(2): myRatio ------------------------------------------------------------------------ * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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