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st: one-sample logrank test


From   Mark Trappmann <mark.trappmann@uni-konstanz.de>
To   statalist@hsphsun2.harvard.edu
Subject   st: one-sample logrank test
Date   Mon, 16 Jan 2006 16:19:06 +0100

Dear list members,

I am currently trying to calculate a one-sample logrank-test (Gail & Ware 1979, Woolson 1981) for a test of equality between the survivor function of a sample and that of the corresponding population.

I have searched the stata-list archives and the User Group Meetings and came up with 2 results - which are both not satisfactory:

1.) I found a presentation by Pere–Joan Ventura on a User Group Meeting in Spain. There is mentioned a Do-File onesam.do for this purpose, which I cannot find anywhere in the net.

2.) I found a reply to an earlier request: Enzo Coviello mentions equivalence to a test for intercept=0 in a poisson model with offset term log(n_expected) (based on articles by Berry (1983) and a technical report by Therneau and Offord (1999)).
This is more tricky: I tried it and the resulting p-values are plausible. However one thing about them contradicts my intuition of this test:

As an approximation I can calculate a normal (two-sample) logrank-test for equality of the survivor function of my sample and of the population. This approximation should - in my opinion - overestimate the p-value (i.e. underestimate the value of the test-statistic), because it treats the population survivor function as a sample survivor function and thus introduces uncertainty that does not exist. So this approximation should be more conservative than the one-sample test.

However, when I follow Enzo Voviellos advice, I get p-values that are a little bit larger than that of the approximation. I find this disturbing as I think it should be the other way around. So I do not really trust the results.


Therefore I would like to know, if anyone can point me to a stata-implementation of this test.

Thanks in advance
Mark


Dr. Mark Trappmann
Universität Konstanz
Fachbereich Politik und Verwaltungswissenschaften
Fach D92
78457 Konstanz
Raum D306
Tel: 07531-88-2321
http://www.uni-konstanz.de/struktur/fuf/polfak/trappmann



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