@fengyuwuzu wrote:
I am not sure if the data need to meet both condition to apply this explanation.
The upper confidence limit for a quartile q p in PROC LIFETEST is incorrect if these conditions are met:
an event is observed at the largest time
the largest event time is also the first time the survival estimate drops below (1-p) for the 100pth percentile point, given the pointwise upper bounds for the survival estimate have not dropped below (1-p) at previous times
My understanding is that both "these conditions" must be met. (The first criterion alone would also seem to me too weak a condition for SAS to produce "incorrect" results from version 9.2 until 9.4 TS1M6, i.e., over many years.) Moreover, I suspect that the two conditions are only necessary conditions for the error to occur: If I'm not mistaken, the almost trivial example of just two survival times t1=1, t2=2, both uncensored, meets both conditions for p=0.75 and yet the upper confidence limit (=2) for that quartile, as obtained with SAS 9.4TS1M5 (SAS/STAT 14.3) using conftype=linear, matches what I get from the formula in the documentation.
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