Non-parametric Tests Flashcards
Why rank the data?
Reduces impact of outliers
Non parametric test
‘Assumption free tests’
These tests generally based on ranking
Statistical power
The ability of a test to find a genuine effect
Non parametric tests have less
Power than parametric only if the sampling distribution is normal.
Type I error is set at
5%
What tests do you use to compare 2 independent conditions?
Wilcoxon rank-sum test and Mann-Witney test
Wilcoxon’s rank-sum test and Mann-Whitney test are non parametric test equivalent to the
Independent t-test
Wilcoxon rank-sum test is
The sum of the ranks in the group that contains fewer people. When equal groups it’s the smaller summed rank
Wilcoxons rank-sum test looks for
Differences between 2 independent samples. Tests whether populations in conditions are from same location.
Mann-Whitney test looks for
Differences btwn 2 independent samples same as Wilcoxon one
What does the kolmogorov-smirnov test test?
If a sample is from a normally distributed population
Other tests similar to Mann-Whitney test are:
Kolmogorov smirnov Z
Moses extreme reactions
Waldorf-wolfowitz runs
In the Mann-Whitney test the group that has the highest mean rank should have…
A greater number of scores within it and vice versa
What is effect size?
Quantitative measure of the strength if a phenomenon
Examples of effect size
Correlation btwn 2 variables
Wilcoxon’s test is reported using a
W
Mann-Whitney’s test is reported using a
U
With both Wilcoxon and Mann-Whitney tests if the sample is small (<50) look at row labelled
exact sig.
In Mann-Whitney and Wilcoxon tests the values of the mean ranks tell
How the groups differ ( group with highest scores will have highest mean rank)
Wilcoxon signed ranked test is used where there are
2 sets of scores to compare - both from same participants
Wilcoxon signed ranked test is the:
Non parametric equivalent to the paired samples t-test
Wilcoxon signed ranked test measures
The difference btwn scores in the 2 conditions
Test statistic for Wilcoxon signed ranked test is
T
