Ted Pedersen

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.