Home > freetb4matlab > outliers > dixontest.m

# dixontest

## PURPOSE

% Dixon tests for outlier

## SYNOPSIS

function [pval,Q] = dixontest(x,type,opposite,twosided)

## DESCRIPTION

```% Dixon tests for outlier
%
% Description:
%
%      Performs several variants of Dixon test for detecting outlier in
%      data sample.
%
% Usage:
%
%      [pval,Q] = dixontest(x,type,opposite,twosided)
%
% Arguments:
%
%        x: a numeric vector or matrix of data values. Each column of a
%           matrix is treated as independent sample set.
%
% opposite: a logical (0,1) indicating whether you want to check not the value
%           with  largest difference from the mean, but opposite (lowest,
%           if most suspicious is highest etc.). Default 0.
%
%     type: an integer specyfying the variant of test to be performed.
%           Possible values are compliant with these given by Dixon
%           (1950): 10, 11, 12, 20, 21. If this value is set to zero, a
%           variant of the test is chosen according to sample size (10
%           for 3-7, 11 for 8-10, 21 for 11-13,  22 for 14 and more). The
%           lowest or highest value is selected automatically, and can be
%           reversed used 'opposite' parameter.
%
% two.sided: treat test as two-sided (default=1).
%
% Details:
%
%      The p-value is calculating by interpolation using 'dixoncdf' and
%      'qtable'. According to Dixon (1951) conclusions, the critical
%      values can be obtained numerically only for n=3. Other critical
%      values are obtained by simulations, taken from original Dixon's
%      paper, and regarding corrections given by Rorabacher (1991).
%
% Value:
%
%     Q: the value of Dixon Q-statistic.
%
%      pval: the p-value for the test.
%
% Author(s):
%
%      Lukasz Komsta, ported from R package 'outliers'.
%    See R News, 6(2):10-13, May 2006
%
% References:
%
%      Dixon, W.J. (1950). Analysis of extreme values. Ann. Math. Stat.
%      21, 4, 488-506.
%
%      Dixon, W.J. (1951). Ratios involving extreme values. Ann. Math.
%      Stat. 22, 1, 68-78.
%
%      Rorabacher, D.B. (1991). Statistical Treatment for Rejection of
%      Deviant Values: Critical Values of Dixon Q Parameter and Related
%      Subrange Ratios at the 95 percent Confidence Level. Anal. Chem.
%      83, 2, 139-146.
%```

## CROSS-REFERENCE INFORMATION

This function calls:
• dixoncdf % This function is simple wrapper to dixoninv with 'rev=1' parameter.
• dixontest % Dixon tests for outlier
This function is called by:

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