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From "Phil Steitz (JIRA)" <j...@apache.org>
Subject [jira] [Closed] (MATH-1247) Kolmogorov-Smirnov exactP gives incorrect p-values for some D-statistics
Date Mon, 06 Jul 2015 00:52:04 GMT

     [ https://issues.apache.org/jira/browse/MATH-1247?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Phil Steitz closed MATH-1247.
-----------------------------
    Resolution: Duplicate

> Kolmogorov-Smirnov exactP gives incorrect p-values for some D-statistics
> ------------------------------------------------------------------------
>
>                 Key: MATH-1247
>                 URL: https://issues.apache.org/jira/browse/MATH-1247
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.4.1
>            Reporter: Phil Steitz
>            Priority: Minor
>             Fix For: 4.0, 3.5
>
>
> The exactP method in KolmogorovSmirnovTest, which is used by default for small samples
in 2-sample tests, can give slightly incorrect p-values in some cases.  The reason for this
is that p(D > d) is computed by examining all m-n partitions and counting the number of
partitions that give D values larger than the observed value.  D values are not rounded, so
some values that are mathematically identical to the observed value compare less than or greater
than it.  This results in small errors in the reported p-values.



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