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st: Pitfall with ctset (survival)


From   "Allan Reese (Cefas)" <allan.reese@cefas.co.uk>
To   "'Statalist \(E-mail\)" <statalist@hsphsun2.harvard.edu>
Subject   st: Pitfall with ctset (survival)
Date   Mon, 17 Sep 2007 16:15:21 +0100

The following problem is confirmed by Tech Support and is still present in v10.

Using ctset (Survival manual v9, p10) you can provide variables of failed, censored and entered.  In my example, the KM plot (after ctset, cttost, sts graph) showed all groups ending at zero survival, which was wrong as failures+censored did not account for all entered.  After some head scratching, I noticed the warning on p14 "entering and exiting must balance".  But there was no error flag, and the analysis appears to proceed by assuming all unaccounted entities failed on the last recorded time.

When failed+censored is greater than entered, a red error message is generated, not when failed+censored<entered.

The solution was to add observations for the censored values at termination of the study.

The workround is to check manually that failed+censored=entered.  A code fix will be provided in v10, and should be editable into v9. 

Allan


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