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From |
n p <nik_padazis@yahoo.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: AW: Survival with time varying covariates |

Date |
Fri, 1 Aug 2003 00:06:54 -0700 (PDT) |

Thanks to Ben Jann for the detailed response Nikos Pantazis Biostatistician --- "Jann, Ben" <ben.jann@soz.gess.ethz.ch> wrote: > Assume -id- indicates the subjects (in all > datasets), -a.dta- contains your demographic data, > -b.dta- and -c.dta- are the marker1 and marker2 > datasets, respectively. The variables -m1- and -m2- > contain the values of the measurements of the > markers 1 and 2, respectively. -t- ist the time of > measurement in both marker datasets, -time- is the > time of the event (in a.dta), -fail- indicates > failure event vs. censored, x1, x2 ... are > covariates. To summarize: > > a.dta: id time fail x1 x2 ... > b.dta: id t m1 > c.dta: id t m2 > > If you only want to use one marker, do the > following: > > . use b > . sort id t > . save bb, replace > . use a > . sort id > . joinby id using bb > . sort id t /* just to be sure */ > . by id: replace time=t[_n+1] if _n!=_N > . by id: replace fail=0 if _n!=_N > > If the measurement of the marker has occured after > time zero, you can either assume that the marker has > been constant up to the first measurement (A) or > treat the case to be left censored (B). > > A: > > . stset time, id(id) failure(fail) > . stcox m1 x1 x2 ... > > B: > > . stset time, id(id) failure(fail) enter(t) > . stcox m1 x1 x2 > > If you need to use both markers, things are a little > more complicated. First combine b.dta and c.dta, > fill in some gaps and joinby (assuming that there > are no simultaneous measurements of marker1 and > marker2; you'd have to modify the code if there are > simultaneous measurements): > > . use b > . append using c > . sort id t > . by id: replace m1=m1[_n-1] if m1==. > . by id: replace m2=m2[_n-1] if m2==. > . save bc, replace > . use a > . sort id > . joinby id using bc > . sort id t /* just to be sure */ > . by id: replace time=t[_n+1] if _n!=_N > . by id: replace fail=0 if _n!=_N > > Then, again the two possibilities A (constant) and B > (left censored): > > A: > > . gsort id -t > . by id: replace m1=m1[_n-1] if m1==. > . by id: replace m2=m2[_n-1] if m2==. > . sort id t > . stset time, id(id) failure(fail) > . stcox m1 m2 x1 x2 ... > > B: > > . stset time, id(id) failure(fail) enter(t) > . stcox m1 m2 x1 x2 ... > > I hope this works. Didn't test it. > > ben > > > > -----Ursprüngliche Nachricht----- > > Von: n p [mailto:nik_padazis@yahoo.com] > > Gesendet: Donnerstag, 31. Juli 2003 13:29 > > An: statalist@hsphsun2.harvard.edu > > Betreff: st: Survival with time varying covariates > > > > > > Hi Stata users, > > > > I need your help in the following problem. I want > to > > perform a survival analysis (via Cox PH models) > where > > some covariates (e.g. demographics) are constant > over > > study time while others (Marker1 and Marker2) are > > periodically measured (usually after time zero > and > > not simultaneously). Thus I have 3 datasets > > > > a) 1 record per subject, with time of event or > > censoring and other not time varying covariates > > b) n1 records per subject for repeated > measurements of > > marker1 (time and value of measurement) > > c) n2 records per subject for repeated > measurements of > > marker2 (time and value of measurement) > > > > The effect of both markers on the hazard is the > main > > question in this study. > > > > I checked the manual's example "Stanford heart > > transplant data" and the "stsplit" command. I also > > checked "stegen" and "stcoxtvc" using "findit time > > varying covariates" but I am still puzzled with > this. > > Is there an easy way to prepare the data at least > for > > one of the two markers? How can I deal with the > > unknown markers' values between time zero and > their > > first measurement? > > > > I am using Stata 7 on a 2.4 GHz 512 RAM WinXP > machine. > > > > Thanks in advance for any help. > > > > Nikos Pantazis > > Biostatistician > > > > > > __________________________________ > > Do you Yahoo!? > > Yahoo! SiteBuilder - Free, easy-to-use web site > design software > > http://sitebuilder.yahoo.com > > * > > * For searches and help try: > > * > http://www.stata.com/support/faqs/res/findit.html > > * http://www.stata.com/support/statalist/faq > > * http://www.ats.ucla.edu/stat/stata/ > > > > * > * For searches and help try: > * > http://www.stata.com/support/faqs/res/findit.html > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ __________________________________ Do you Yahoo!? Yahoo! SiteBuilder - Free, easy-to-use web site design software http://sitebuilder.yahoo.com * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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