Text::NSP::Measures::2D::CHI::tscore 1.03

Text::NSP::Measures::2D::CHI::tscore is a Perl module that implements T-score measure of association for bigrams.

SYNOPSIS

Basic Usage

use Text::NSP::Measures::2D::CHI::tscore;

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

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

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

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 T-score is defined as a ratio of difference between the observed and the expected mean to the variance of the sample. Note that this is a variant of the standard t-test that was proposed for use in the identification of collocations in large samples of text.

Thus, the T-score is defined as follows:

m11 = n1p * np1 / npp

T-score = (n11 - m11)/sqrt(n11)

calculateStatistic() - method to calculate the tscore Coefficient

INPUT PARAMS : $count_values .. Reference of an hash containing the count values computed by the count.pl program.
RETURN VALUES : $tscore .. tscore value for this bigram.
getStatisticName() - Returns the name of this statistic
INPUT PARAMS : none
RETURN VALUES : $name .. Name of the measure.