/ 
Statistics-Sequences-0.041
River stage one • 5 direct dependents • 5 total dependents
/ Statistics::Sequences::Joins

NAME

Statistics::Sequences::Joins - the Wishart-Hirshfeld test of dichotomous sequences

SYNOPSIS

use Statistics::Sequences::Joins;
$joins = Statistics::Sequences::Joins->new();
$joins->load(qw/0 0 1 0 0 0 1 0 0 0 0 1 1 0 0 0 1 1 1 1 0 0/);
$joins->test()->dump();

DESCRIPTION

Superficially, this test is very similar to the Runs Test. A join is a point in a sequence of dichotomous data where the values alternate. For example, in the following series

0 0 1 0 0 0 1 0 0 0 0 1 1 0 0 0 1 1 1 1 0 0

there is a join (of the values 0 and 1) at the indices of 1 and 2, then immediately another join (of the values 1 to 0) at 2 and 3, and then another join at 5 and 6. (Continuing, there are eight joins in total in this series.) The only difference between joins and runs, then, is that joins are counted at the point of alternation, whereas runs are counted for each unique segment (between the alternations). So joins will always be at least 1 less the number of runs.

The test-statistics, however, differ more fundamentally. Runs are tested on the basis of the observed distribution (e.g., of hits and misses), whereas joins are tested on the basis of a theoretically expected distribution.

METHODS

Methods are essentially as described in Statistics::Sequences. See this manpage for how to handle non-dichotomous data, e.g., numerical data, or those with more than two categories; the relevant methods are not described here.

new

$join = Statistics::Sequences::Joins->new();

Returns a new Joins object. Expects/accepts no arguments but the classname.

load

$joins->load(@data);
$joins->load(\@data);
$joins->load('sample1' => \@data1, 'sample2' => \@data2)
$joins->load({'sample1' => \@data1, 'sample2' => \@data2})

Loads data anonymously or by name. See load in the Statistics::Sequences manpage.

test

$joins->test(prob => 1/3);

Test the currently loaded data for significance of the number of joins, given a probability of each state in the data array of prob. This parameter is optionally defined in the call to test; the default value is 0.5. Valid values are between 0 and 1, inclusive. In a classic signal detection task, for instance, where a state is either a hit or miss, the probability of each state is 0.5. In a classic ESP task, with 5 possible alternatives as targets on each trial, each state has a 1 in 5 chance of occurring, but we still test for a probability of 1/2 as the data will be have to be reduced to a dichotomous hit/miss format in order to be Runs- or Joins-tested.

dump

$joins->dump(flag => '1|0', text => '0|1|2');

Print Joins-test results to STDOUT. See dump in the Statistics::Sequences manpage for details.

EXAMPLE

Here the problem is to assess the degree of consistency of ESP scoring from the number of hits obtained in each of 200 runs of 25 trials each. The number of hits expected on the basis of chance is 5 per run. To test for sustained high or low scoring sequences, a join is defined as the point at which a score on one side of this expectation value is followed by a score on the other side. Ignoring scores equalling the expectation value of 5, the probability of a join is 1/2, or 0.5 (the default value to test), assuming that, say, a score of 4 is as likely as a score of 6, and anything greater than a deviation of 5 (from 5) is improbable (or impossible). A meaningful result would obtain when the number of joins observed was below the number expected; we ignore the converse (and perverse) situation.

use Statistics::Sequences;

# Conduct 200 pseudo-ESP runs:
my ($i, $hits, $target, $response, @scores);
foreach ($i = 0; $i < 200; $i++) {
   $hits = 0;
   for (0 .. 24) {
       $target = (qw/star plus wave square circle/)[int(rand(5))];
       $response = (qw/star plus wave square circle/)[int(rand(5))];
       $hits++ if $target eq $response;
   }
   $scores[$i] = $hits;
 }

 my $expected_hits = 5;

 my $seq = Statistics::Sequences->new();
 $seq->load(@scores);
 $seq->cut(value => $expected_hits, equal => 0);
 $seq->test(what => 'joins', tails => 1, ccorr => 1)->dump(text => 1, flag => 1);
 # prints, e.g., Joins: expected = 79.00, observed = 67.00, z = -1.91, p = 0.028109*

REFERENCES

Burdick, D. S., & Kelly, E. F. (1977). Statistical methods in parapsychological research. In B. B. Wolman (Ed.), Handbook of Parapsychology (pp. 81-130). New York, NY, US: Van Nostrand Reinhold.

Wishart, J. & Hirshfeld, H. O. (1936). A theorem concerning the distribution of joins between line segments. Journal of the London Mathematical Society, 11, 227.

SEE ALSO

Statistics::Sequences::Runs : An analoguous and more widely known test.

Statistics::Sequences::Pot : Another concept of sequences.

BUGS/LIMITATIONS

No computational bugs as yet identfied. Hopefully this will change, given time.

REVISION HISTORY

See CHANGES in installation dist for revisions.

AUTHOR/LICENSE

rgarton AT cpan DOT org

This program is free software. It may be used, redistributed and/or modified under the same terms as Perl-5.6.1 (or later) (see http://www.perl.com/perl/misc/Artistic.html).

Disclaimer

To the maximum extent permitted by applicable law, the author of this module disclaims all warranties, either express or implied, including but not limited to implied warranties of merchantability and fitness for a particular purpose, with regard to the software and the accompanying documentation.