NAME
Text::NSP::Measures::2D::CHI::phi  Perl module that implements Phi coefficient measure for bigrams.
SYNOPSIS
Basic Usage
use Text::NSP::Measures::2D::CHI::phi;
my $phi = Text::NSP::Measures::2D::CHI::phi>new();
my $npp = 60; my $n1p = 20; my $np1 = 20; my $n11 = 10;
$phi_value = $phi>calculateStatistic( n11=>$n11,
n1p=>$n1p,
np1=>$np1,
npp=>$npp);
if( ($errorCode = $phi>getErrorCode()))
{
print STDERR $erroCode."  ".$phi>getErrorMessage();
}
else
{
print $phi>getStatisticName."value for bigram is ".$phi_value;
}
DESCRIPTION
This function computes the the square of the traditional formulation of the Phi Coefficient.
Assume that the frequency count data associated with a bigram <word1><word2> is stored in a 2x2 contingency table:
word2 ~word2
word1 n11 n12  n1p
~word1 n21 n22  n2p

np1 np2 npp
where n11 is the number of times <word1><word2> occur together, and n12 is the number of times <word1> occurs with some word other than word2, and n1p is the number of times in total that word1 occurs as the first word in a bigram.
PHI^2 = ((n11 * n22)  (n21 * n21))^2/(n1p * np1 * np2 * n2p)
Note that the value of PHI^2 is equivalent to Pearson's ChiSquared test multiplied by the sample size, that is:
ChiSquared = npp * PHI^2
We use PHI^2 rather than PHI since PHI^2 was employed for collocation identification in:
Church, K. (1991) Concordances for Parallel Text, Seventh Annual Conference of the UW Centre for the New OED and Text Research, Oxford, England.
 calculateStatistic()  method to calculate the Phi Coefficient

INPUT PARAMS : $count_values .. Reference of an hash containing the count values computed by the count.pl program.
RETURN VALUES : $phi .. phi value for this bigram.
 getStatisticName()  Returns the name of this statistic

INPUT PARAMS : none
RETURN VALUES : $name .. Name of the measure.
AUTHOR
Ted Pedersen, University of Minnesota Duluth <tpederse@d.umn.edu>
Satanjeev Banerjee, Carnegie Mellon University <satanjeev@cmu.edu>
Amruta Purandare, University of Pittsburgh <amruta@cs.pitt.edu>
Bridget ThomsonMcInnes, University of Minnesota Twin Cities <bthompson@d.umn.edu>
Saiyam Kohli, University of Minnesota Duluth <kohli003@d.umn.edu>
HISTORY
Last updated: $Id: phi.pm,v 1.10 2006/06/17 18:03:19 saiyam_kohli Exp $
BUGS
SEE ALSO
@inproceedings{GaleC91,
author = {Gale, W. and Church, K.},
title = {A Program for Aligning Sentences in Bilingual Corpora},
booktitle = {Proceedings of the 29th Annual Meeting of the
Association for Computational Linguistics},
address = {Berkeley, CA},
year = {1991}
url = L<http://www.cs.mu.oz.au/acl/J/J93/J931004.pdf>}
http://groups.yahoo.com/group/ngram/
http://www.d.umn.edu/~tpederse/nsp.html
COPYRIGHT
Copyright (C) 20002006, Ted Pedersen, Satanjeev Banerjee, Amruta Purandare, Bridget ThomsonMcInnes and Saiyam Kohli
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program; if not, write to
The Free Software Foundation, Inc.,
59 Temple Place  Suite 330,
Boston, MA 021111307, USA.
Note: a copy of the GNU General Public License is available on the web at http://www.gnu.org/licenses/gpl.txt and is included in this distribution as GPL.txt.