Text::NSP::Measures::2D::MI::ps 1.03

Text::NSP::Measures::2D::MI::ps is a Perl module that implements Poisson-Stirling measure of association for bigrams.

SYNOPSIS

Basic Usage

use Text::NSP::Measures::2D::MI::ps;

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

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

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

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 > as shown by 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

The poisson stirling measure is a negative lograthimic approximation of the poisson-likelihood measure. It uses the stirlings firmula to approximate the factorial in poisson-likelihood measure.

Posson-Stirling = n11 * ( log(n11) - log(m11) - 1)

which is same as

Posson-Stirling = n11 * ( log(n11/m11) - 1)

Methods

calculateStatistic() - This method calculates the ps value

INPUT PARAMS : $count_values .. Reference of an hash containing the count values computed by the count.pl program.

RETURN VALUES : $poissonStirling .. Poisson-Stirling value for this bigram.

getStatisticName() - Returns the name of this statistic

INPUT PARAMS : none

RETURN VALUES : $name .. Name of the measure.

Product's homepage

Requirements:

· Perl