NAME

Text::NSP::Measures::4D - Perl module that provides basic framework for building measure of association for 4-grams.

SYNOPSIS

This module can be used as a foundation for building 4-dimensional measures of association that can then be used by statistic.pl. In particular this module provides methods that give convenient access to 4-d (i.e., 4-gram) frequency counts as created by count.pl, as well as some degree of error handling that verifies the data.

Basic Usage

  use Text::NSP::Measures::4D::MI::ll;

  $ll_value = calculateStatistic( 
                                  n1111=>8,
                                  n1ppp=>306,
                                  np1pp=>83,
                                  npp1p=>83,
                                  nppp1=>57,
                                  n11pp=>8,
                                  n1p1p=>8,
                                  n1pp1=>8,
                                  np11p=>83,
                                  np1p1=>56,
                                  npp11=>56,
                                  n111p=>8,
                                  n11p1=>8,
                                  n1p11=>8,
                                  np111=>56,
                                  npppp=>15180);

  if( ($errorCode = getErrorCode()))
  {
    print STDERR $erroCode." - ".getErrorMessage()."\n";
  }
  else
  {
    print getStatisticName."value for 4-gram is ".$ll_value."\n";
  }

DESCRIPTION

The methods in this module retrieve observed 4-gram frequency counts and marginal totals, and also compute expected values. They also provide support for error checking of the output produced by count.pl. These methods are used in all the 4-gram (4d) measure modules provided in NSP. If you are writing your own 4d measure, you can use these methods as well.

With 4-gram or 4d measures we use a 4x4 contingency table to store the frequency counts associated with each word in the trigram, as well as the number of times the trigram occurs. The notation we employ is as follows:

Marginal Frequencies:

 n1ppp = the number of ngrams where the first word is word1.
 np1pp = the number of ngrams where the second word is word2.
 npp1p = the number of ngrams where the third word is word3
 nppp1 = the number of ngrams where the fourth word is word4
 n2ppp = the number of ngrams where the first word is not word1. 
 np2pp = the number of ngrams where the second word is not word2.
 npp2p = the number of ngrams where the third word is not word3.
 nppp2 = the number of ngrams where the fourth words is not word4

Observed Frequencies:

 n1111 = number of times word1, word2 and word3 occur together in
         their respective positions, joint frequency.
 n1112 = number of times word1, word 2 and word3 occur in their respective
         positions but word4 does not.
 n1121 = number of times word1, word2 and word4 occur in their respective
         positions but word3 does not.
 n1122 = number of times word1 and word2 occur in their repsective positions
         but word3 and word4 do not.
 n1211 = number of times word1, word3 and word4 occur in their respective 
         positions but word2 does not.
 n1212 = number of times word1 and word3 occur in their respective positions
         but word2 and word4 do not.
 n1221 = number of times word1 and word4 occur in their respective positions
         but word2 and word3 do not
 n1222 = number of times word1 occurs in its respective position but word2, 
         word3 and word4 do not.
 n2111 = number of times word2, word3 and word4 occur in their respective 
         positions but word1 does not.
 n2112 = number of times word2 and word3 occur in their respective positions
         but word1 and word4 do not.
 n2121 = number of times word2 and word4 occur in their respective positions
         but word1 and word3 do not.
 n2122 = number of times word2 occurs in its respective position but word1, 
         word3 and word4 do not.
 n2211 = number of times word3 and word4 occur in their respective positions
         but word1 and word2 do not.
 n2212 = number of times word3 occurs in its respective position but word1, 
         word2 and word4 do not.
 n2221 = number of times word4 occurs in its respective position but word1,
         word2, and word3 do not.
 n2222 = number of times neither word1, word2, word3 or word4 occur in their
         respective positions.

Expected Frequencies:

 m1111 = expected number of times word1, word2 and word3 occur together in
         their respective positions, joint frequency.
 m1112 = expected number of times word1, word 2 and word3 occur in their respective
         positions but word4 does not.
 m1121 = expected number of times word1, word2 and word4 occur in their respective
         positions but word3 does not.
 m1122 = expected number of times word1 and word2 occur in their repsective positions
         but word3 and word4 do not.
 m1211 = expected number of times word1, word3 and word4 occur in their respective 
         positions but word2 does not.
 m1212 = expected number of times word1 and word3 occur in their respective positions
         but word2 and word4 do not.
 m1221 = expected number of times word1 and word4 occur in their respective positions
         but word2 and word3 do not
 m1222 = expected number of times word1 occurs in its respective position but word2, 
         word3 and word4 do not.
 m2111 = expected number of times word2, word3 and word4 occur in their respective 
         positions but word1 does not.
 m2112 = expected number of times word2 and word3 occur in their respective positions
         but word1 and word4 do not.
 m2121 = expected number of times word2 and word4 occur in their respective positions
         but word1 and word3 do not.
 m2122 = expected number of times word2 occurs in its respective position but word1, 
         word3 and word4 do not.
 m2211 = expected number of times word3 and word4 occur in their respective positions
         but word1 and word2 do not.
 m2212 = expected number of times word3 occurs in its respective position but word1, 
         word2 and word4 do not.
 m2221 = expected number of times word4 occurs in its respective position but word1,
         word2, and word3 do not.
 m2222 = expected number of times neither word1, word2, word3 or word4 occur in their
         respective positions.
=head2 Methods

computeObservedValues($count_values) - A method to compute observed values, and also to verify that the computed Observed values are correct, That is they are positive, less than the marginal totals and the total bigram count.: INPUT PARAMS : $count_values .. Reference to an hash consisting of the count values passed to the calculateStatistic() method.
RETURN VALUES : 1/undef ..returns '1' to indicate success and an undefined(NULL) value to indicate failure.
computeExpectedValues($count_values) - A method to compute expected values.: INPUT PARAMS : $count_values .. Reference to an hash consisting of the count output.
RETURN VALUES : 1/undef ..returns '1' to indicate success and an undefined(NULL) value to indicate failure.
computeMarginalTotals($marginal_values) - This method computes the marginal totals from the valuescomputed by the count.pl program and are passed to the calculateStatistic() method.: INPUT PARAMS : $count_values .. Reference to an hash consisting of the frequency combination output.
RETURN VALUES : 1/undef ..returns '1' to indicate success and an undefined(NULL) value to indicate failure.

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 <bthomson@cs.umn.edu>

Saiyam Kohli, University of Minnesota Duluth <kohli003@d.umn.edu>

HISTORY

Last updated: $Id: 4D.pm,v 1.3 2010/11/12 18:40:23 btmcinnes Exp $

BUGS

COPYRIGHT

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