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Date: Wed, 24 Aug 2005 10:04:56 -0400
From: John Gant <john.gant@gmail.com>
To: Jakarta Commons Developers List <commons-dev@jakarta.apache.org>
Subject: Re: DO NOT REPLY [Bug 36331] - [math] spearman rank cross correlation
In-Reply-To: <20050824134330.5522A126@ajax.apache.org>
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References: <20050824134330.5522A126@ajax.apache.org>

Specifically testTwo() in
http://issues.apache.org/bugzilla/attachment.cgi?id=3D16172  takes care
of data with equal value (ie equal rank), is this the type of
situation to which you are referring? Yes I agree, we should implement
routines to sort in more diverse ways, but for right now I depend upon
Arrays.sort() to perform the sorting.

Thanks,
John

On 8/24/05, bugzilla@apache.org <bugzilla@apache.org> wrote:
> DO NOT REPLY TO THIS EMAIL, BUT PLEASE POST YOUR BUG=B7
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>=20
> http://issues.apache.org/bugzilla/show_bug.cgi?id=3D36331
>=20
>=20
>=20
>=20
>=20
> ------- Additional Comments From brent@worden.org  2005-08-24 15:43 -----=
--
> I noticed you implementation does not take into account ties in the data.=
  Ties
> can effect the correlation coefficeint to a great degree.
>=20
> A nice approach to address ties is to rank the data adjusting the ranks o=
f tied
> elements and then compute the Pearson's correlation coefficient on the ra=
nkings.
>=20
> See http://web.uccs.edu/lbecker/SPSS/ctabs2.htm#5E.%20Spearman%20Correlat=
ion,%
> 20rs for a brief explaination.
>=20
> If we get into adding more non-parametric routines, I for one would like =
to see
> some general, ranking utililies such as taking an array of data and retur=
ning
> the ranking array.  The ranking could be driven by a tie ranking policy f=
or
> dealing with ties in the data.  The default policy would be to use the me=
an
> rank for ties.  Other policies could be to omit the data, use the highest=
 rank
> or, use the lowest rank.
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--=20
John Gant

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