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From |
Ben Andagalu <ben.andagalu@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Survival analysis multiple events |

Date |
Wed, 26 May 2010 17:40:49 +0000 |

Thanks a lot Ben Andagalu MD On Wed, May 26, 2010 at 3:08 PM, Steve Samuels <sjsamuels@gmail.com> wrote: > There is no need to do _anything_ about the 28 day period if you use > the "conditional risk set model (time from the previous event)" of > section 3.2.4. Just use the dates that you now have. You will need > to add a time0 = 0 to start each interval and a stratum variable to > indicate the number of prior failures. > > You could just as well use time0 = 28. The only difference would be a > shift in the baseline survival curves S(t). In the first formulation, > S(t) = 1 for t<=28 provided there are no failures under treatment. > The Cox model results will not change at all. If you don't > understand why, consult one of the survival references. > > The measurement error in using dates of visits for the dates of events > should average +3.5 days or so. If your period of followup for each > failure is long in comparison, you probably won't introduce much bias > into the Cox parameters. To get more accurate baseline curves, apply > the average correction (-3 or -4) to the date of visit. This will > center the measurement error closer to zero. > > Steve > > On Wed, May 26, 2010 at 10:23 AM, Ben Andagalu <ben.andagalu@gmail.com> wrote: >> My intention was to use the Cox regression model taking into account >> potential clustering of events at the individual level. >> The "not at risk" is due to the treatment given after experiencing the >> event. the failures were detected at weekly follow-ups and unplanned >> visits >> I had actually read section 3.2.4 at >> www.stata.com/support/faqs/stat/stmfail.html and other literature >> prior to posting, and my major problem remains to be how to add those >> 28 days. I started using Stata not so long ago, so pardon my >> ignorance. >> Thanks >> Ben Andagalu, MD >> >> On Wed, May 26, 2010 at 1:31 PM, Steve Samuels <sjsamuels@gmail.com> wrote: >>> >>> The 28 day problem aside, what analyses did you have in mind? >>> Someone can be "not at risk" for different reasons, and the specific >>> setting could affect the choice of analysis. >>> >>> Have you read www.stata.com/support/faqs/stat/stmfail.html ? Your data >>> are almost set up for the "conditional risk set model (time from the >>> previous event)" , discussed in section 3.2.4. This model resets the >>> clock after each failure. You can do Cox regression, and baseline >>> survival curves computed for the time period after each failure will >>> remain at 1.0 for at least 28 days. >>> >>> This model would not be appropriate if you believe that risk of >>> failure is much more strongly related to time since enrollment than to >>> time from previous failure. If you need another model, -snapspan- >>> will convert your data to a format that -stset- can use, You might >>> consider withdrawing people from observation in the 28 day period >>> after each failure. You do this by adding 28 days to the start date of >>> the interval. The resulting survival curves and inference will refer >>> to people who are conceptually "at risk" for the entire time after >>> enrollment, even if this was not true of the people under study. The >>> section in the Stata Survival manual on -stset- has many examples >>> >>> There could be another issue. Is the "date of follow-up" visit the >>> date a failure occurred or did the failure occur at an unknown date >>> prior to the visit? If the latter, you have either grouped data, if >>> the follow-up visits are at fixed times from enrollment, or >>> interval-censored data, if the follow-up intervals are not the same >>> for all people. >>> >>> >>> Good references are: >>> 1) Stephen Jenkins's text Survival Analysis using Stata: >>> http://www.iser.essex.ac.uk/survival-analysis >>> 2) An Introduction To Survival Analysis Using Stata (Paperback) >>> by Mario A. Cleves William W. Gould , and Roberto G. Gutierrez >>> >>> Steve >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> On Tue, May 25, 2010 at 3:23 PM, <ben.andagalu@gmail.com> wrote: >>> > How do i go about setting up dataset to analyse multiple failures per individual with a 28 day 'not at risk' period after each failure? individuals were followed up weekly after randomization - The variables i have are: date of randomization, date of follow-up visit, visit id, failure event , patient id, and the predictor variables. The data is in the 'long' format. Thanks. Ben Andagalu. >>> > >>> > >>> > * >>> > * 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/ >>> > >>> >>> >>> >>> -- >>> Steven Samuels >>> sjsamuels@gmail.com >>> 18 Cantine's Island >>> Saugerties NY 12477 >>> USA >>> Voice: 845-246-0774 >>> Fax: 206-202-4783 >>> >>> * >>> * 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/ >> > > > > -- > Steven Samuels > sjsamuels@gmail.com > 18 Cantine's Island > Saugerties NY 12477 > USA > Voice: 845-246-0774 > Fax: 206-202-4783 > > * > * 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/

**References**:**st: Survival analysis multiple events***From:*ben.andagalu@gmail.com

**Re: st: Survival analysis multiple events***From:*Steve Samuels <sjsamuels@gmail.com>

**Re: st: Survival analysis multiple events***From:*Ben Andagalu <ben.andagalu@gmail.com>

**Re: st: Survival analysis multiple events***From:*Steve Samuels <sjsamuels@gmail.com>

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