st: RE: Puzzling behavior in -sts graph- with tmax()

["Visintainer, Paul" <Paul.Visintainer@baystatehealth.org>]

Just for the record. I think we figured out the behavior of -sts graph- with the tmax() option.  The issue seems to be my use a time point in tmax() that doesn't correspond to an event time the function.  That is, even with an arbitrary time entered tmax(), -sts graph- only plots the graph at the times where an event occurred (either a failure or loss).  Looking at the survivor function table (-sts list-), the event times jump from 28 to 32.  Between times 28 and 32, nothing happened -- no failures and no losses.  So using -sts graph- with tmax(29) or tmax(30) or tmax(31), will produce the same graphic as tmax(28).  Since there was a failure at 28 days, the graph shows a failure without any ongoing censoring.

-p

________________________________________________
Paul F. Visintainer, PhD
Baystate Medical Center
Springfield, MA 01199

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Visintainer, Paul
Sent: Wednesday, October 19, 2011 9:17 AM
To: 'statalist@hsphsun2.harvard.edu'
Subject: st: Puzzling behavior in -sts graph- with tmax()

-sts graph- with option tmax() seems to show inconsistent graphing behavior.  This issue was raised in 2007, but all I could find as a solution was a work-around using -sts gen-, then plotting with -scatter-.  

Here is the inconsistency:

use http://www.stata-press.com/data/r12/drug2b, clear

.sts g  -- plots the last observation as censored to time 39.

.sts g, tmax(35) - appropriately plots to 35 with the last obs as censored

.sts g, tmax(30) - plots to 28 with last obs as terminal, not censored at 30

.sts g, tmax(20) - plots to 20 with last obs as censored


While the difference at time 30 is small (only plotted to time 28 and does not show censoring), in my dataset the discrepancy is quite large.  I'm trying to truncate the plot at 50 days, but -sts graph- will only plot to 10 days.

Am I interpreting this incorrectly?

Thanks.
________________________________________________
Paul F. Visintainer, PhD
Baystate Medical Center


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