Text::NSP::Measures::2D::CHI - Perl module that provides error checks for the Pearson's chi squared, phi coefficient and the Tscore measures.
use Text::NSP::Measures::2D::CHI::x2; my $npp = 60; my $n1p = 20; my $np1 = 20; my $n11 = 10; $x2_value = calculateStatistic( n11=>$n11, n1p=>$n1p, np1=>$np1, npp=>$npp); if( ($errorCode = getErrorCode())) { print STDERR $errorCode." - ".getErrorMessage()."\n""; } else { print getStatisticName."value for bigram is ".$x2_value."\n""; }
This module is the base class for the Chi-squared and Phi coefficient measures. This module provides error checks specific for these measures, it also implements the computations that are common to these measures.
x2 = 2 * [((n11 - m11)/m11)^2 + ((n12 - m12)/m12)^2 + ((n21 - m21)/m21)^2 + ((n22 -m22)/m22)^2]
PHI^2 = ((n11 * n22) - (n21 * n21))^2/(n1p * np1 * np2 * n2p)
tscore = (n11 - m11)/sqrt(n11)
Note that the value of PHI^2 is equivalent to Pearson's Chi-Squared test multiplied by the sample size, that is:
Chi-Squared = npp * PHI^2 Although T-score seems quite different from the other two measures we have put it in the CHI family because like the other two measures it uses the difference between the observed and expected values and is also quite similar in ranking the bigrams.
INPUT PARAMS : $count_values .. Reference of an hash containing the count values computed by the count.pl program.
RETURN VALUES : 1/undef ..returns '1' to indicate success and an undefined(NULL) value to indicate failure.
INPUT PARAMS : $n ..Observed value $m ..Expected value
RETURN VALUES : (n-m)^2/m ..the log of the ratio of observed value to expected value.
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 Thomson-McInnes, University of Minnesota Twin Cities <bthompson@d.umn.edu>
Saiyam Kohli, University of Minnesota Duluth <kohli003@d.umn.edu>
Last updated: $Id: CHI.pm,v 1.14 2008/03/26 17:18:26 tpederse Exp $
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Copyright (C) 2000-2006, Ted Pedersen, Satanjeev Banerjee, Amruta Purandare, Bridget Thomson-McInnes and Saiyam Kohli
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