Text::NSP::Measures::2D::CHI.3pm

Langue: en

Version: 2006-06-21 (mandriva - 01/05/08)

Section: 3 (Bibliothèques de fonctions)

Sommaire

NAME

Text::NSP::Measures::2D::CHI - Perl module that provides error checks
                               for the Pearsons chi squared, phi coefficient
                               and the Tscore measures.

SYNOPSIS

Basic Usage 
   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"";
   }

DESCRIPTION

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.
Pearson's Chi-Squared
   x2 = 2 * [((n11 - m11)/m11)^2 + ((n12 - m12)/m12)^2 +
            ((n21 - m21)/m21)^2 + ((n22 -m22)/m22)^2]
Phi Coefficient
  PHI^2 = ((n11 * n22) - (n21 * n21))^2/(n1p * np1 * np2 * n2p)
T-Score
  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 obseved and expected values and is also
  quite similar in ranking the bigrams.
getValues() - This method calls the computeMarginalTotals(), computeObservedValues() and the computeExpectedValues() methods to compute the observed and expected values. It checks thes values for any errors that might cause the PHI and x2 measures to fail.
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
                                    faliure.

computeVal() - Computes the deviation in observed value with respect to the expected values
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.

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 Thomson-McInnes, University of Minnesota Twin Cities
                             <bthompson@d.umn.edu>

Saiyam Kohli, University of Minnesota Duluth
                             <kohli003@d.umn.edu>

HISTORY

Last updated: $Id: CHI.pm,v 1.13 2006/09/15 23:27:03 saiyam_kohli Exp $

BUGS

SEE ALSO

<http://groups.yahoo.com/group/ngram/>

<http://www.d.umn.edu/~tpederse/nsp.html>

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.