Re: st: Survival analysis multiple events

[Steve Samuels <sjsamuels@gmail.com>]

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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