Text::NSP::Measures::3D::MI::ll.3pm

Langue: en

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

Section: 3 (Bibliothèques de fonctions)

Sommaire

NAME

Text::NSP::Measures::3D::MI::ll - Perl module that implements Loglikelihood
                                  measure of association for trigrams.

SYNOPSIS

Basic Usage 
   use Text::NSP::Measures::3D::MI::ll;
 
 

   $ll_value = calculateStatistic( n111=>10,
                                   n1pp=>40,
                                   np1p=>45,
                                   npp1=>42,
                                   n11p=>20,
                                   n1p1=>23,
                                   np11=>21,
                                   nppp=>100);
 
 

   if( ($errorCode = getErrorCode()))
   {
     print STDERR $erroCode." - ".getErrorMessage()."\n";
   }
   else
   {
     print getStatisticName."value for bigram is ".$ll_value."\n";
   }

DESCRIPTION

The log-likelihood ratio measures the devitation between the observed data and what would be expected if <word1>, <word2> and <word3> were independent. The higher the score, the less evidence there is in favor of concluding that the words are independent.

The expected values for the internal cells are calculated by taking the product of their associated marginals and dividing by the sample size, for example:

             n1pp * np1p * npp1
    m111=   --------------------
                    nppp

Then the deviation between observed and expected values for each internal cell is computed to arrive at the log-likelihood value.

  Log-Likelihood = 2 * [n111 * log(n111/m111) + n112 * log(n112/m112) +
            n121 * log(n121/m121) + n122 * log(n122/m122) +
            n211 * log(n211/m211) + n212 * log(n212/m212) +
            n221 * log(n221/m221) + n222 * log(n222/m222)]

Methods

calculateStatistic($count_values) - This method calculates the ll value
INPUT PARAMS : $count_values .. Reference of an hash containing
                                       the count values computed by the
                                       count.pl program.

RETURN VALUES : $loglikelihood .. Loglikelihood value for this trigram.

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: ll.pm,v 1.9 2006/06/21 11:10:53 saiyam_kohli Exp $

BUGS

SEE ALSO

   @article{Dunning93,
             author = {Dunning, T.},
             title = {Accurate Methods for the Statistics of
           Surprise and Coincidence},
             journal = {Computational Linguistics},
             volume = {19},
             number = {1},
             year = {1993},
             pages = {61-74}
             url = L<http://www.comp.lancs.ac.uk/ucrel/papers/tedstats.pdf>}
 
 

   @inproceedings{moore:2004:EMNLP,
                 author    = {Moore, Robert C.},
                 title     = {On Log-Likelihood-Ratios and the Significance of Rare
               Events },
                 booktitle = {Proceedings of EMNLP 2004},
                 editor = {Dekang Lin and Dekai Wu},
                 year      = 2004,
                 month     = {July},
                 address   = {Barcelona, Spain},
                 publisher = {Association for Computational Linguistics},
                 pages     = {333--340}
                 url = L<http://acl.ldc.upenn.edu/acl2004/emnlp/pdf/Moore.pdf>}

<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.