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From |
Steve Samuels <sjsamuels@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: comparing 25th percentile survival time between two race groups |

Date |
Fri, 28 Sep 2012 17:26:10 -0400 |

Dear Haena: > > On Sep 28, 2012, at 2:43 PM, Haena Lee wrote: > > Hi Listers, > I have tried to produce the median survival time and its 95% CI with > renal transplant data. "Stci" command, however, did not produce any > median values. So I generated the graph of median survival time by > race (African American vs. White) and the graph showed it only reached > to the length of 25% in the course of follow-up, indicating both of > groups have died not even near 50% (median), but mostly near the > length of 25% tile in the course of follow-up. > What you observe can be better phrased as saying that followup was not long enough to observe 50% of failures. > 1. Given this, I attempted to produce 25th percentile survival time. > However I am struggling with comparing the difference of 25th > percentile survival time between African American and White across 10 > regions in US. The command that I used: > sort UNOS > by UNOS: stci , by(race_all) p(25) > > I was trying to use "ranksum" but it doesn't have an option for > testing differences of other percentiles besides median. Which command > should I use? That's a correct command. It tests for any difference where survival in one group is better, not just differences in medians. > > 2. In comparing the median to the 25 percentile, there are some > regions where the length to 25% tile is significantly longer than > median. In this case, what would you guys do? If you would choose to > use median survival time, then what else could I do in order not only > to produce the median survival time and 95% CI, but to test the > difference of median survival time between groups instead stci (since > it didn't produce in previous analysis)? Your observation is impossible in theory; to persuade us, you'd need to follow the advice in Statalist FAQ (3.3) and show us the commands and results that lead you to this observation. If I had to guess, I'd say that you looked at the Kaplan-Meier survival curve, not at -stci- results. A survival curve shows the proportion of people who haven't had the event at a time, not the proportion who have failed. Thus the point corresponding to the 25% mark on the y axis is where 25% of people haven't failed and 75% have. In other words it is the 75th percentile for failure. To see the failure time percentiles, the command is: ******************* sts graph, failure ******************* You might benefit from reading a good text on survival data, e.g. Cleves et al. (2010). Reference: Cleves, Mario, William Gould, Roberto Gutierrez, and Yulia Marchenko. 2010. An Introduction to Survival Analysis Using Stata, Third Edition. College Station, Tex: Stata Press. Steve > Thank you so much! * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/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/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: comparing 25th percentile survival time between two race groups***From:*Haena Lee <hannahlee419@gmail.com>

**References**:**st: comparing 25th percentile survival time between two race groups***From:*Haena Lee <hannahlee419@gmail.com>

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