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st: problem obtaining hazard estimates

From   "Steinar Fossedal" <>
To   <>
Subject   st: problem obtaining hazard estimates
Date   Tue, 22 May 2007 16:02:04 +0200

Hi, listers

I am experiencing problems obtaining a Kaplan-Meier estimate of the
hazard function. Using -sts graph, haz- returns an error "Variable __ub
not found" r(111). The error does not, however, appear when requesting
the surivival function of the same data. I can reproduce the error using
the leukemia data from stata-press (see printout below), even after a
complete reinstall of Stata 9. How complete it actually was is hard to
tell, my settings were still identical to what they were prior to the
reinstall even though I renamed the old "C:\Program Files\Stata9-folder"
to Stata9_old. Where else does Stata store information?

Until now I have been using -sts gen haz=h- instead, but today, by a one
time fluke, stata suddenly returned different results compared to
earlier. I would normally be willing to write this off as some fault on
my part had it not been for the disturbing fact that the fluke-results
were a lot more in sync with the predictions from my models. The results
are, however, not reproducable in the same session even after doing no
changes to the dataset.

I am now wondering if the two problems are somehow related, and fear
there is something wrong with the hazard-estimates I have been
recieving. Can someone confirm the problem, or suggest a way to handle



. use, clear
(Leukemia Remission Study)

. stset weeks, failure(relapse)

     failure event:  relapse != 0 & relapse < .
obs. time interval:  (0, weeks]
 exit on or before:  failure

       42  total obs.
        0  exclusions
       42  obs. remaining, representing
       30  failures in single record/single failure data
      541  total analysis time at risk, at risk from t =         0
                             earliest observed entry t =         0
                                  last observed exit t =        35

. sts graph

         failure _d:  relapse
   analysis time _t:  weeks

. sts graph, haz

         failure _d:  relapse
   analysis time _t:  weeks
variable __ub not found

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