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Text::NSP::Measures::2UseriContributed Perl Text::NSP::Measures::2D::Fisher(3)

NAME
Text::NSP::Measures::2D::Fisher - Perl module that provides methods
to compute the	Fishers	exact tests.

SYNOPSIS
Basic Usage

use Text::NSP::Measures::2D::Fisher::left;

my \$npp = 60; my \$n1p = 20; my	\$np1 = 20;  my \$n11 = 10;

\$left_value = calculateStatistic( n11=>\$n11,
n1p=>\$n1p,
np1=>\$np1,
npp=>\$npp);

if( (\$errorCode = getErrorCode()))
{
print STDERR	\$errorCode." - ".getErrorMessage();
}
else
{
print getStatisticName."value for bigram is ".\$left_value;
}

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 fishers exact tests are calculated by fixing	the marginal totals
and computing the hypergeometric	probabilities for all the possible
contingency tables,

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.

A right 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 greater than or equal to	the
given value. A right sided Fisher's Exact Test tells us how likely it
is to randomly sample a table where n11 is greater than observed. In
other words, it tells us	how likely it is to sample an observation
where the two words are more dependent than currently observed.

A two-tailed fishers test is calculated by adding the probabilities of
all the contingency tables with probabilities less than the probability
of the observed table. The two-tailed fishers test tells	us how likely
it would	be to observe an contingency table which is less probable than
the current table.

Methods
getValues() -This method	calls the computeObservedValues() and the
computeExpectedValues() methods to compute the observed and marginal
total values. It	checks these values for	any errors that	might cause
the Fishers Exact test measures to fail.
INPUT PARAMS	 : \$count_values       .. Reference of an array
containing
the count values computed by
the
count.pl program.

RETURN VALUES : 1/undef	     ..returns '1' to indicate success
and an undefined(NULL) value to
indicate
failure.

computeDistribution() - This method calculates the probabilities	for
all the possible	tables
INPUT PARAMS	 : \$n11_start	       .. the value for	the cell 1,1
in the first	contingency
table
\$final_limit	       .. the value of cell 1,1	in the
last	contingency table
for which we have to compute
the probability.

RETURN VALUES : \$probability	       .. Reference to a hash
containing hypergeometric
probabilities	for all	the
possible contingency
tables

AUTHOR
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>

HISTORY
Last updated: \$Id: Fisher.pm,v 1.21 2008/03/26 17:18:26 tpederse	Exp \$

BUGS
<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

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.

Note: a copy of the GNU General Public License is available on the web
at <http://www.gnu.org/licenses/gpl.txt>	and is included	in this
distribution as GPL.txt.

perl v5.24.1			  2008-03-26Text::NSP::Measures::2D::Fisher(3)

NAME | SYNOPSIS | DESCRIPTION | AUTHOR | HISTORY | BUGS | SEE ALSO | COPYRIGHT

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