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From | Austin Nichols <austinnichols@gmail.com> |
To | statalist@hsphsun2.harvard.edu |
Subject | Re: st: Median survival times via Poisson model, using -margins- ? |
Date | Tue, 26 Mar 2013 10:28:22 -0400 |
Andrew Lover <graupel75@gmail.com>: Why not: use http://www.pauldickman.com/survival/diet, clear gen t=dox - doe stset t stci if hieng==1, by(job) ? Do your example data not represent what you actually have? On Mon, Mar 25, 2013 at 10:55 PM, <graupel75@gmail.com> wrote: > Dear 'Listers, > > I have found multiple references to calculating median survival times > for sub-populations from Poisson survival models (eg. Kelsey JK, > Whittemore AS, Evans AS, Thompson WD. Methods in observational > epidemiology. 2nd ed. New York: Oxford University Press, 1996, pgs. > 31-3). A general scheme reported is : > > We computed mu as the unweighted average of these 18 death rates [Per > categorical from Poisson model]. The risk of death at time t, R(t), > was computed as R(t) = 1 - e ^-(mu*t), where t was in years. Median > survival was computed by finding the value of t satisfying the > relation, R(t) = 1 - e ^-(mu * t) = 0.5. > > I suspect *anything* is possible using -margins- but am stymied on how > to get there with confidence intervals for the median times. > > A (not very interesting or well-modelled) example: > > ***** Start example ***** > use http://www.pauldickman.com/survival/diet, clear > > gen survdays = dox - doe > gen survyear = survdays/365.25 > stset survyear, failure(chd == 1) id(id) > > stsplit, at(fail) > > collapse (sum) survyear chd, by(hieng job) > sum surv, detail > > nbreg chd hieng i.job, exposure(survyear) irr > > // margins > > ***** End example ***** > > Any thoughts on how to predict median survival times with 95% CIs for > the three levels of 'job' at say, hieng ==1? * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/