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From |
"Dupont, William" <william.dupont@Vanderbilt.Edu> |

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

Subject |
st: Sub-optimal smoothing behavior by stcurve? |

Date |
Fri, 18 Nov 2005 10:46:20 -0600 |

Statalisters I believe that the smoothing behavior for the hazard function plots of -stcurve- is less than ideal near the time boundaries. Consider the program given below, which performs two analyses on the -drugtr- data set from stata-press. Analysis A shows a marked and steady increase in hazard at times between 13 and 21. Analysis B is the same as analysis A except that all observations have been censored at time 17. The hazard curves from these analyses are similar until about time 13. At later times, hazard A increases sharply while hazard B decreases sharply. I wonder if the latter behavior is due to the fact that the smoothing algorithm at time 13 looks at some interval symmetric about 13, recognizes that there are no failures to the right of 13 but fails to see that there are no patients at risk at later times either. I have not attempted to read the -stcurve- code and realize that devising smoothing algorithms can be non-trivial. I wondered, however, if the program was really working as the authors intended or it there might be some way of improving its performance near the time boundaries. Bill William D. Dupont phone: 615-343-4100 URL http://biostat.mc.vanderbilt.edu/twiki/bin/view/Main/WilliamDupont *********************************** * Example of sub-optimal smoothing near a boundary for stcurve * log using stcurve.log, replace set more on use http://www.stata-press.com/data/r9/drugtr, clear stset tabulate died * * Analysis A * stcox drug, basehc(a) stcurve, hazard outfile(a, replace) more replace died = died & studytime <= 17 replace studytime = min(17, studytime) stset tabulate died * * Analysis B * stcox drug, basehc(b) stcurve, hazard outfile(b, replace) more * * Graph hazard estimates from both analyses together * use b, clear rename haz1 hazcensored merge _t using a, sort sort _t line haz1 hazcensored _t, xlabel(0(5)30) xtick(0(1)33) log close * * 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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