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From |
Haena Lee <hannahlee419@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

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

Date |
Fri, 28 Sep 2012 18:04:52 -0500 |

Thank you Steve, That's really good point to look at the graph especially for the failures. According to ranksum, I was not able to find an option for 25th percentiles. When I was comparing the differences of median survival time between African American and White across 10 different regions in US, I used this following command; . sort UNOS . by UNOS: ranksum d_enrollment, by(race_all) In this case, I didn't need to let Stata know it is median survival time because I guess median was default. However my question is how I can particularly tell Stata that it is to test 25th percentiles this time. Any help? Thanks much. On Fri, Sep 28, 2012 at 4:26 PM, Steve Samuels <sjsamuels@gmail.com> wrote: > 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/ -- ===================== Haena Lee Ph.D Student Sociology Department The University of Chicago 312 - 405 - 3223 * * 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:*Steve Samuels <sjsamuels@gmail.com>

**Re: st: comparing 25th percentile survival time between two race groups***From:*Steve Samuels <sjsamuels@gmail.com>

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

**Re: st: comparing 25th percentile survival time between two race groups***From:*Steve Samuels <sjsamuels@gmail.com>

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