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Re: st: using stcox with clustered data

From   Ricardo Ovaldia <>
Subject   Re: st: using stcox with clustered data
Date   Tue, 1 Oct 2002 11:50:32 -0700 (PDT)

--- "Seidel, Kristy" <> wrote:

> I have been asked to come up with a plan for
> analyzing an unusual clinical
> data set that consists of paired time-to-event
> observations.  The setting is
> an infant intensive care unit (IICU).  The research
> question is:  which of
> two topical medications is better at shortening the
> duration of diaper rash
> in IICU patients. Because there is so much
> variability in the types of
> problems that infants are admitted to the IICU with,
> the investigators wish
> to use a paired design in which the nursing staff
> will use medication A on
> one side of the infant's rear and medication B on
> the other side.  Each
> subject would then contribute two observations, time
> to resolution of rash
> on side A and time to resolution on side B.  The
> times to resolution within
> individual are likely to be strongly correlated.
> They also expect a fair
> degree of censoring in this setting -- up to half of
> the study subjects may
> be discharged from the IICU prior to resolution of
> rash on one or both
> sides.   

Take a look at Mario Cleves' excellent write-up in
STB-49, ssa13 "Analysis of multiple failure-time data
with Stata". Specifically entry: 3.1.1 "Unordered
failure events of the same type". You can also find a
copy of this document in the Stata FAQ section. Here
is the URL:



Center for Applied Research
University Hospital
Oklahoma City,OK

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