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Text-NSP-0.73
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/ leftFisher

NAME

leftFisher.pm

SYNOPSIS

Statistical library package to calculate the Fisher's exact test (left-sided). This package should be used with statistic.pl and rank.pl

DESCRIPTION

A left sided test is calculated by adding the probabilities of all the possible two by two contingency tables formed by fixing the marginal totals and changing the value of n11 to less than the given value. A left sided Fisher's Exact Test tells us how likely it is to randomly sample a table where n11 is less than observed. In other words, it tells us how likely it is to sample an observation where the two words are less dependent than currently observed.

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.

A user reported observing some cases of overflow in Fisher's exact test in the Ngram Statistics Package (both the left and right variations). My own conclusion is that there is a bit of rounding error at work here, since we are summing together a potentially large number of hyper-geometric probabilities to arrive at the value.

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.