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
giuseppe.cardillo-edta@poste.it
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