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From |
"Kieran McCaul" <Kieran.McCaul@uwa.edu.au> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
RE: st: Adjusted Kaplan-Meier curves |

Date |
Tue, 9 Jun 2009 10:13:54 +0800 |

.. 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/ > > ----------------------------------------- > > > > > > > > > > * > > * For searches and help try: > > * http://www.stata.com/help.cgi?search > > * http://www.stata.com/support/statalist/faq > > * http://www.ats.ucla.edu/stat/stata/ > > > > > > > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > > > > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**RE: st: Adjusted Kaplan-Meier curves***From:*Ricardo Ovaldia <ovaldia@yahoo.com>

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