Name

Statistics::ChisqIndep - The module to perform chi-square test of independence (a.k.a. contingency tables)

Synopsis

            

              
              
#example for Statistics::ChisqIndep
use strict;
use Statistics::ChisqIndep;
use POSIX;
# input data in the form of the array of array references
my @obs = ([15, 68, 83], [23,47,65]);
my $chi = new Statistics::ChisqIndep;
$chi->load_data(\@obs);
# print the summary data along with the contingency table
$chi->print_summary();  
#print the contingency table only
$chi->print_contingency_table(); 
#the following output is the same as calling the function of print_summary
#all of the detailed info such as the expected values, degree of freedoms 
#and totals are accessible as object globals  
#check if the load_data() call is successful
if($chi->{valid}) {  
  print "Rows: ", $chi->{rows}, "\n"; 
  print "Columns: ", $chi->{cols}, "\n"; 
  print "Degree of Freedom: ", $chi->{df}, "\n";
  print "Total Count: ", $chi->{total}, "\n";
  print "Chi-square Statistic: ", 
        $chi->{chisq_statistic}, "\n";
  print "p-value: ", $chi->{p_value}, "\n";
  print "Warning: 
        some of the cell counts might be too low.\n" 
    if ($chi->{warning});
  #output the contingency table
  my $rows = $chi->{rows};  # # rows
  my $cols = $chi->{cols};  # # columns
  my $obs = $chi->{obs}; # observed values 
  my $exp = $chi->{expected}; # expected values 
  my $rtotals = $chi->{rtotals}; # row totals 
  my $ctotals = $chi->{ctotals}; #column totals 
  my $total = $chi->{total}; # total counts
  for (my $j = 0; $j < $cols; $j++) {
    print "\t",$j + 1;
  }
  print "\trtotal\n"; 
  for (my $i = 0; $i < $rows; $i ++) {
    print $i + 1, "\t"; 
    for(my $j = 0 ; $j < $cols; $j ++) {
     #observed values can be accessed
     #in the following way 
     print $obs->[$i]->[$j], "\t";  
    }
    #row totals can be accessed
    # in the following way
    print $rtotals->[$i], "\n";
    print "\t";
    for(my $j = 0 ; $j < $cols; $j ++) {
     #expected values can be accessed 
     #in the following way
     printf "(%.2f)\t", $exp->[$i]->[$j];
    }
    print "\n"; 
  }
  print "ctotal\t";
  for (my $j = 0; $j < $cols; $j++) {
    #column totals can be accessed in the following way
    print $ctotals->[$j], "\t";
  }
  #output total counts
  print $total, "\n";
}
            
          

Description

            

              
              
This is the module to perform the Pearson's Chi-squared test on contingency tables of 2 dimensions. The users input the observed values in the table form and the module will compute the expected values for each cell based on the independence hypothesis. The module will then compute the chi-square statistic and the corresponding p-value based on the observed and the expected values to test if the 2 dimensions are truly independent.
            
          

AUTHOR

            

              
              
Yun-Fang Juan , Yahoo! Inc. 
yunfang@yahoo-inc.com 
yunfangjuan@yahoo.com
            
          

SEE ALSO

Statistics::Distributions