Text::NSP::Measures::3D::MI::ps - Perl module that implements Poisson Stirling Measure for trigrams.
use Text::NSP::Measures::3D::MI::ps; $ps_value = calculateStatistic( n111=>10, n1pp=>40, np1p=>45, npp1=>42, n11p=>20, n1p1=>23, np11=>21, nppp=>100); if( ($errorCode = getErrorCode())) { print STDERR $erroCode." - ".getErrorMessage()."\n"; } else { print getStatisticName."value for bigram is ".$ps_value."\n"; }
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
The poisson stirling measure is a negative lograthimic approximation of the poisson-likelihood measure. It uses the stirlings firmula to approximate the factorial in poisson-likelihood measure. It is computed as follows:
Posson-Stirling = n111 * ( log(n111) - log(m111) - 1)
INPUT PARAMS : $count_values .. Reference of an hash containing the count values computed by the count.pl program.
RETURN VALUES : $poissonStirling .. Poisson-Stirling value for this trigram.
INPUT PARAMS : none
RETURN VALUES : $name .. Name of the measure.
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: ps.pm,v 1.7 2006/06/21 11:10:53 saiyam_kohli Exp $
@inproceedings{ church89word, author = {Kenneth W. Church and Patrick Hanks}, title = {Word association norms, mutual information, and Lexicography}, booktitle = {Proceedings of the 27th. Annual Meeting of the Association for Computational Linguistics}, publisher = {Association for Computational Linguistics}, address = {Vancouver, B.C.}, pages = {76--83}, year = {1989}, url = L<http://acl.ldc.upenn.edu/J/J90/J90-1003.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
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