From allwrigh at maths.ox.ac.uk  Tue Dec 15 18:05:09 2009
From: allwrigh at maths.ox.ac.uk (allwrigh at maths.ox.ac.uk)
Date: Tue, 15 Dec 2009 18:05:09 +0100 (CET)
Subject: [Rd] apparently incorrect p-values from 2-sided Kolmogorov-Smirnov
	test (PR#14145)
Message-ID: <20091215170510.225BA282EFEA@mail.pubhealth.ku.dk>

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I am using R version 2.6.2 (2008-02-08) on a Ubuntu Linux system.
I seemed to be finding occasional errors in the p-values produced by 
ks.test(a,b) when a and b were vectors of 10 to 20 values.
So I tried to find simpler examples, and one that illustrates what I mean 
is included below and as the attached typescript file.
It is just

x<-1:5
y<-c(2.5,4.5)
ks.test(x,y)

The value of the D_2,5 statistic is calculated as 0.4 correctly, but the 
p-value is stated by R as 1, though in fact it should be 20/21=0.9524
As I say this is just one example of quite a lot of errors of this kind 
that I am finding.
If you want more examples I can try to be more systematic about tracking 
them down.
Thank you,
David Allwright.
-----------------------------------------------------------------------------
Dr DJ Allwright              E-mail    : allwrigh at maths.ox.ac.uk
OCIAM(Oxford Centre for Industrial and Applied Mathematics)
Mathematical Institute       Telephone : [+44](0)1865-280604
24-29 St.Giles'              FAX                     -270515
Oxford OX1 3LB, UK. 
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Script started on Tue 15 Dec 2009 16:49:46 GMT
]0;swamp-thing: ~/smithinst/be2swamp-thing:be2% R

R version 2.6.2 (2008-02-08)
Copyright (C) 2008 The R Foundation for Statistical Computing
ISBN 3-900051-07-0

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> x<-1:5
> y<-c(2.5,4.5)
> ks.test(x,y)

 	Two-sample Kolmogorov-Smirnov test

data:  x and y 
D = 0.4, p-value = 1
alternative hypothesis: two-sided

> q()
Save workspace image? [y/n/c]: n
]0;swamp-thing: ~/smithinst/be2swamp-thing:be2% exit 
exit

Script done on Tue 15 Dec 2009 16:50:13 GMT

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[Rd] apparently incorrect p-values from 2-sided Kolmogorov-Smirnov test (PR#14145)
allwrigh at maths.ox.ac.uk