NAME

odds.pm

SYNOPSIS

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

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 odds ratio computes the ratio of the number of times that the words in a bigram occur together (or not at all) to the number of times the words occur individually. It is the cross product of the diagonal and the off-diagonal.

Thus, ODDS RATIO = n11*n22/n21*n12

if n21 and/or n12 is 0, then each zero value is "smoothed" to one to avoid a zero in the denominator.

AUTHORS

Ted Pedersen <tpederse@d.umn.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

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.