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RE: st: Predicting survival at a specific time following generalized gamma regression


From   "Feiveson, Alan H. (JSC-SK311)" <alan.h.feiveson@nasa.gov>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Predicting survival at a specific time following generalized gamma regression
Date   Wed, 11 Jul 2012 09:05:50 -0500

Thanks Steve - I was not familiar with -predictnl- I suspected there had to be an easier way!

Al

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Steve Samuels
Sent: Wednesday, July 11, 2012 9:01 AM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: Predicting survival at a specific time following generalized gamma regression


Instead of

*******************
predict t_surv, surv
********************

try
*****************************************
predictnl t_surv = predict(surv),  ///
se(se_surv) ci(low_surv up_surv)
*****************************************



Steve
sjsamuels@gmail.com


On Jul 11, 2012, at 7:24 AM, Thomas Inns wrote:

Hello,

If someone could kindly take the time to help me I'd be very appreciative. I'm try to predict the probability of survival at one year following infection.
I'm using a parametric survival model with a generalized gamma distribution and an accelerated failure-time metric (streg, distribution(gamma) time).

I have used the streg postestimation command "predict, surv", but I can't work out how to put a confidence interval around my predicted survival probability at one year following infection. Is this possible? And if so, do you know how I might do this?

Below is my code, inspired by Bobby Gutierrez's post at http://www.stata.com/statalist/archive/2010-12/msg00647.html.

Thanks,
Thomas Inns

*************CODE BEGINS*************
streg i.ribolog i.gender i.agetri i.year i.ftbin##i.trustapp, d(gamma) time

****predict conditional survivor function (probability of survival past time t)
****(time t = 1 year)
*prediction at t = 365.25
gen tt = 365.25

*keep old _t
gen t_old = _t

*put in _t you want to use for prediction
replace _t = tt

*predict surival past time _t (one year)
predict t_surv, surv

label var t_surv "gamma prediction"

*summarise these predictions
summ t_surv, detail
**************CODE ENDS**************


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