NAME

Text::NSP::Measures::2D::CHI::tscore - Perl module that implements T-score
measure of association for bigrams.

SYNOPSIS

Basic Usage

  use Text::NSP::Measures::2D::CHI::tscore;
  my $npp = 60; my $n1p = 20; my $np1 = 20;  my $n11 = 10;
  $tscore_value = calculateStatistic( n11=>$n11,
                                      n1p=>$n1p,
                                      np1=>$np1,
                                      npp=>$npp);
  if( ($errorCode = getErrorCode()))
  {
    print STDERR $errorCode." - ".getErrorMessage()."\n"";
  }
  else
  {
    print getStatisticName."value for bigram is ".$tscore_value."\n"";
  }

DESCRIPTION

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.

The T-score is defined as a ratio of difference between the observed and the expected mean to the variance of the sample. Note that this is a variant of the standard t-test that was proposed for use in the identification of collocations in large samples of text.

Thus, the T-score is defined as follows:

    m11 = n1p * np1 / npp
    T-score = (n11 - m11)/sqrt(n11)

calculateStatistic() - method to calculate the tscore Coefficient

INPUT PARAMS : $count_values .. Reference of an hash containing
the count values computed by the
count.pl program.

RETURN VALUES : $tscore .. tscore 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 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: tscore.pm,v 1.11 2006/06/21 11:10:52 saiyam_kohli Exp $

BUGS

SEE ALSO

  @incollection {ChurchGHH91,
          author={Church, K. and Gale, W. and Hanks, P. and Hindle, D. },
          title={Using Statistics in Lexical Analysis},
          booktitle={Lexical Acquisition: Exploiting On-Line Resources
                      to Build a Lexicon},
          editor={Zernik, U.},
          year={1991},
          address={Hillsdale, NJ},
          publisher={Lawrence Erlbaum Associates}
          url = L<http://www.patrickhanks.com/papers/usingStats.pdf>}

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

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

COPYRIGHT

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.