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st: RE: RE: Varying survival distributions & interval censoring (2)


From   siyama@who.int
To   statalist@hsphsun2.harvard.edu
Subject   st: RE: RE: Varying survival distributions & interval censoring (2)
Date   Wed, 23 Jun 2004 14:22:02 +0200

Many thanks Stephen, I will try your suggestion and perhaps compare outputs
to those of SAS PROC LIFEREG 

http://ftp.sas.com/techsup/download/sample/samp_lib/statsampDocumentation_Ex
amples_f00000060.html

http://v8doc.sas.com/sashtml/


All the best,

Amani





-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Stephen P Jenkins
Sent: 23 June 2004 13:04
To: statalist@hsphsun2.harvard.edu
Subject: st: RE: Varying survival distributions & interval censoring (2)

> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of 
> siyama@who.int
> Sent: 23 June 2004 11:07
> To: statalist@hsphsun2.harvard.edu
> Subject: st: Varying survival distributions & interval censoring (2)
> 
> 
> My thanks to Stephen Jenkins for his pointer below, I found the notes 
> quite detailed and helpful.
> 
> The "Discrete" entry in the [ST] Manual reads:
> 
> Discrete-time survival analysis concerns analysis of time-to-event 
> data whenever survival times are either
> (a) intrinsically discrete (e.g. numbers of machine cycles), or
> (b) grouped into discrete intervals of time ("interval censoring"). If 
> intervals are of equal length, then the same methods can be applied to 
> both
> (a) and (b): survival times are positive integers.
> 
> In the data set I am handling, every subject has his/her OWN interval 
> of time, that is their actual failure happens between two home-visit 
> dates that the fieldworker makes.  The home-visit dates allow us to 
> calculate the exact ages of the subjects who fall in one of 3 
> categories:
> 
> i.	Left-censored: the fieldworker initiates the home visits and
> observes the failure has already taken place.
> 
> ii.	Interval-censored: failure has take place between two 
> home visits,
> and the fieldworker has record of both 	dates.
> 
> iii.	Right-censored: the fieldworker completes the last home 
> visit and
> failure has not been observed.
> 
> 
> I am not sure exactly on how to structure the data to reflect the 
> 3-states above to use with "streg" or a similar model that would allow 
> me to vary the distribution of the failure time (between exponential, 
> weibull, lognormal, loglogistic and generalised gamma).


If I understand you correctly, you won't be able to use -streg-. You will
have to program yourself, using -ml-, where the sample log-likelihood
expression will include a number of different components corresponding to
each of (i)-(iii) above. [The text by Klein and Moeschberger, /Survival
Analysis/ has a taxonomy of different likelihood contribution types for the
different types of spell that you mention.] At the stage at which you
characterise the contributions, you will have to also decide which failure
time distribution to assume.

Stephen
-------------------------------------------------------------
Professor Stephen P. Jenkins <stephenj@essex.ac.uk> Institute for Social and
Economic Research University of Essex, Colchester CO4 3SQ, U.K.
Tel: +44 1206 873374.  Fax: +44 1206 873151.
http://www.iser.essex.ac.uk   



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