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Text-NSP-0.73
River stage one • 2 direct dependents • 3 total dependents
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/ ll

NAME

ll.pm

SYNOPSIS

Statistical library package to calculate the Loglikelihood ratio. This package should be used with statistic.pl and rank.pl.

DESCRIPTION

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

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

          np1 * n1p
   m11=   ---------
            npp

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

 Log-Likelihood = 2 * [n11 * log(n11/m11) + n12 * log(n12/m12) + 
                       n21 * log(n21/m21) + n22 * log(n22/m22)]

AUTHORS

Ted Pedersen <tpederse@d.umn.edu>

Satanjeev Banerjee <banerjee@cs.cmu.edu>

Bridget Thomson McInnes <bthomson@d.umn.edu>

BUGS

This measure currently only defined for bigram data stored in 2x2 contingency table.

SEE ALSO

Mailing List: http://groups.yahoo.com/ngram

COPYRIGHT

Copyright 2000-2004 by Ted Pedersen and Satanjeev Banerjee

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.