Wilcoxon

non parametric Wilcoxon test for two paired samples

Non parametric Wilcoxon test to evaluate the difference between paired (dependent) samples.
If the number of difference is less than 15, the algorithm calculate the exact ranks distribution;
else it uses a normal distribution approximation.
Now, the MatLab function SIGNRANK returns the same p-value.
Anyway, this Wilcoxon function gives a more detailed output (that is necessary for publications...)
Syntax: STATS=WILCOXON(X1,X2,PLTS)

Inputs:
X1 and X2 - data vectors.
ALPHA - significance level (default = 0.05).
PLTS - Flag to set if you don't want (0) or want (1) view the plots
Outputs:
- W value and p-value when exact ranks distribution is used.
- W value, Z value, Standard deviation (Mean=0), p-value when normal distribution is used
If STATS nargout was specified the results will be stored in the STATS
struct.

Example:

X1=[77 79 79 80 80 81 81 81 81 82 82 82 82 83 83 84 84 84 84 85 85 86 86 87 87];

X2=[82 82 83 84 84 85 85 86 86 86 86 86 86 86 86 86 87 87 87 88 88 88 89 90 90];

Calling on Matlab the function: wilcoxon(X1,X2)

Answer is:

WILCOXON TEST

Mean_of_differences Confidence_interval
___________________ ___________________

Binomial_estimator 3 3 4
Hodges_Lehmann_estimator 3.5 3 4

Sample size is good enough to use the normal distribution approximation

W Mean SD Z p_value_two_tails
___ ____ ______ ______ _________________

325 0 73.161 4.4354 9.1886e-06

Created by Giuseppe Cardillo
[e-mail]

To cite this file, this would be an appropriate format:
Cardillo G. (2006). Wilcoxon test: non parametric Wilcoxon test for paired samples.
http://www.mathworks.com/matlabcentral/fileexchange/12702