Re: st: Survival analysis multiple events

[Ben Andagalu <ben.andagalu@gmail.com>]

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.
> >
> >
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> >
>
>
>
> --
> Steven Samuels
> sjsamuels@gmail.com
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