Manual Reference Pages - TEXT::NSP::MEASURES::2D::CHI::X2 (3)
Text::NSP::Measures::2D::CHI::x2 - Perl module that implements Pearsons
chi squared measure of association for
my $npp = 60; my $n1p = 20; my $np1 = 20; my $n11 = 10;
$x2_value = calculateStatistic( n11=>$n11,
if( ($errorCode = getErrorCode()))
print STDERR $errorCode." - ".getErrorMessage()."\n"";
print getStatisticName."value for bigram is ".$x2_value."\n"";
Pearsons Chi-squred test measures the devitation between the observed
data and what would be expected if <word1> and <word2> were independent.
The higher the score, the less evidence there is in favor of concluding
that the words are independent.
Assume that the frequency count data associated with a bigram
<word1><word2> is stored in a 2x2 contingency table:
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.
The expected values for the internal cells are calculated by taking the
product of their associated marginals and dividing by the sample size,
np1 * n1p
Then the deviation between observed and expected values for each internal
cell is computed to arrive at the Pearsons Chi-Squared test value:
Pearsons Chi-Squared = 2 * [((n11 - m11)/m11)^2 + ((n12 - m12)/m12)^2 +
((n21 - m21)/m21)^2 + ((n22 -m22)/m22)^2]
calculateStatistic() - method to calculate the Chi-squared value.
INPUT PARAMS : $count_values .. Reference of an hash containing
the count values computed by the
RETURN VALUES : $x2 .. x2 value for this bigram.
getStatisticName() - Returns the name of this statistic
INPUT PARAMS : none
RETURN VALUES : $name .. Name of the measure.
Ted Pedersen, University of Minnesota Duluth
Satanjeev Banerjee, Carnegie Mellon University
Amruta Purandare, University of Pittsburgh
Bridget Thomson-McInnes, University of Minnesota Twin Cities
Saiyam Kohli, University of Minnesota Duluth
Last updated: $Id: x2.pm,v 1.10 2006/06/21 11:10:52 saiyam_kohli Exp $
Copyright (C) 2000-2006, Ted Pedersen, Satanjeev Banerjee, Amruta
Purandare, Bridget Thomson-McInnes 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 02111-1307, 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.
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