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RE: st: Adjusted Kaplan-Meier curves


From   Ricardo Ovaldia <ovaldia@yahoo.com>
To   statalist@hsphsun2.harvard.edu
Subject   RE: st: Adjusted Kaplan-Meier curves
Date   Mon, 8 Jun 2009 20:12:11 -0700 (PDT)

Thank you. That may be what they are doing in those articles; adjusting each curve individually. I am not sure if that makes a lot of sense.


Ricardo Ovaldia, MS
Statistician 
Oklahoma City, OK


--- On Mon, 6/8/09, Kieran McCaul <Kieran.McCaul@uwa.edu.au> wrote:

> From: Kieran McCaul <Kieran.McCaul@uwa.edu.au>
> Subject: RE: st: Adjusted Kaplan-Meier curves
> To: statalist@hsphsun2.harvard.edu
> Date: Monday, June 8, 2009, 9:13 PM
> ..
> 
> When you use -adjustfor()- in -sts graph-, the survival
> functions are obtained from a Cox model.
> 
> Suppose you are interested in the effect of a treatment
> (treat, 0=no, 1=yes) adjusted for sex (0=female, 1=male).
> 
> sts graph, by(treat) adjustfor(sex)
> 
> This will produce a graph with two curves that are obtained
> from the baseline survival functions estimated in two Cox
> models:
> 
> xi:stcox i.sex if treat==0
> xi:stcox i.sex if treat==1
> 
> 
> 
> ______________________________________________
> Kieran McCaul MPH PhD
> WA Centre for Health & Ageing (M573)
> University of Western Australia
> Level 6, Ainslie House
> 48 Murray St
> Perth 6000
> Phone: (08) 9224-2701
> Fax: (08) 9224 8009
> email: Kieran.McCaul@uwa.edu.au
> http://myprofile.cos.com/mccaul 
> http://www.researcherid.com/rid/B-8751-2008
> ______________________________________________
> Man is a credulous animal, and must believe something; in
> the absence of good grounds for belief, 
> he will be satisfied with bad ones. Bertrand Russell 
> 
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu]
> On Behalf Of Ricardo Ovaldia
> Sent: Tuesday, 9 June 2009 9:02 AM
> To: statalist@hsphsun2.harvard.edu
> Subject: RE: st: Adjusted Kaplan-Meier curves
> 
> 
> Thank you Kieran. That is what I was thinking. The
> parallelism is cause by the PH assumptions. So the question
> remains. What method is being use in published manuscripts
> that report "Adjusted Kaplan-Meier curves"?
> 
> See for example:
> http://content.nejm.org/cgi/reprint/342/15/1077.pdf
> or
> http://content.nejm.org/cgi/reprint/342/15/1077.pdf
> 
> They claim using Cox to adjust, but the curves are not
> parallel.
> 
> 
> Ricardo Ovaldia, MS
> Statistician 
> Oklahoma City, OK
> 
> 
> --- On Mon, 6/8/09, Kieran McCaul <Kieran.McCaul@uwa.edu.au>
> wrote:
> 
> > From: Kieran McCaul <Kieran.McCaul@uwa.edu.au>
> > Subject: RE: st: Adjusted Kaplan-Meier curves
> > To: statalist@hsphsun2.harvard.edu
> > Date: Monday, June 8, 2009, 7:00 PM
> > The curves generated after a Cox
> > model are always going to be parallel because the Cox
> model
> > assumes proportional hazards.  If your Kaplan-Meier
> > curves are crossing, this could indicate that the
> hazards
> > are not proportional.  It depends where the
> cross-over
> > occurs.  They will often cross-over towards the end
> of
> > follow-up, but that's usually because the data is
> getting
> > sparse and the survival estimates are becoming a bit
> > erratic.  
> > 
> > If the cross-over occurs at a time point where you
> still
> > have a reasonable amount of data, then you need to
> check the
> > proportionality assumption in the Cox model.
> > 
> > ______________________________________________
> > Kieran McCaul MPH PhD
> > WA Centre for Health & Ageing (M573)
> > University of Western Australia
> > Level 6, Ainslie House
> > 48 Murray St
> > Perth 6000
> > Phone: (08) 9224-2701
> > Fax: (08) 9224 8009
> > email: Kieran.McCaul@uwa.edu.au
> > http://myprofile.cos.com/mccaul 
> > http://www.researcherid.com/rid/B-8751-2008
> > ______________________________________________
> > Man is a credulous animal, and must believe something;
> in
> > the absence of good grounds for belief, 
> > he will be satisfied with bad ones. Bertrand Russell 
> > 
> > -----Original Message-----
> > From: owner-statalist@hsphsun2.harvard.edu
> > [mailto:owner-statalist@hsphsun2.harvard.edu]
> > On Behalf Of Ricardo Ovaldia
> > Sent: Tuesday, 9 June 2009 7:33 AM
> > To: statalist@hsphsun2.harvard.edu
> > Subject: Re: st: Adjusted Kaplan-Meier curves
> > 
> > Thank you Maarten.
> > 
> > That is what exactly what I did, except that I used
> the
> > -at()- option to plot one curve for each drug. I used
> the
> > dummies to do that such that for example for drug=1 it
> would
> > be -at(_Idrug_2=0 _Idrug_3=0)- and so on. However the
> curves
> > are parallel, with jumps at every death and do not
> look like
> > the unadjusted curves.
> > 
> > Ricardo.
> >  
> > Ricardo Ovaldia, MS
> > Statistician 
> > Oklahoma City, OK
> > 
> > 
> > --- On Mon, 6/8/09, Maarten buis <maartenbuis@yahoo.co.uk>
> > wrote:
> > 
> > > From: Maarten buis <maartenbuis@yahoo.co.uk>
> > > Subject: Re: st: Adjusted Kaplan-Meier curves
> > > To: statalist@hsphsun2.harvard.edu
> > > Date: Monday, June 8, 2009, 11:12 AM
> > > 
> > > --- On Mon, 8/6/09, Ricardo Ovaldia wrote:
> > > > I have been asked to plot Kaplan-Meier
> curves
> > adjusted
> > > for
> > > > covariates, such as age, gender, race. 
> > > > My thought was to use -stcox- to adjust and
> then
> > plot
> > > the
> > > > adjusted survival using -stcurve-. 
> > > > But I am not sure I am doing this correctly.
> The
> > KM
> > > curves
> > > > plotted with -sts graph,by()- crossover,
> but
> > those
> > > plotted
> > > > with -stcurve- do not and also they have a
> lot
> > more
> > > steps
> > > > than the original curves. Any ideas?
> > > 
> > > Sounds like a reasonable strategy to me. I don't
> have
> > any
> > > concrete ideas, except that I added the example
> below
> > of
> > > how I would do this. Maybe you can see something
> in my
> > 
> > > example that is different from what you did (no
> > guarantees
> > > that what did is better than what you did
> though).
> > > 
> > > *--------- begin example --------
> > > sysuse cancer, clear
> > > stset studytime, failure(died)
> > > xi: stcox i.drug age, basesurv(S)
> > > stcurve, survival
> > > *--------- end example ----------
> > > 
> > > Hope this helps,
> > > Maarten
> > > 
> > > -----------------------------------------
> > > Maarten L. Buis
> > > Institut fuer Soziologie
> > > Universitaet Tuebingen
> > > Wilhelmstrasse 36
> > > 72074 Tuebingen
> > > Germany
> > > 
> > > http://home.fsw.vu.nl/m.buis/
> > > -----------------------------------------
> > > 
> > > 
> > >       
> > > 
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