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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/ > > > ----------------------------------------- > > > > > > > > > > > > > > > * > > > * 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/ > * * 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/

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