Mann-Whitney U and Wilcoxon Signed Rank test Flashcards
What is the Mann-whitney U test?
a non-parametric version of independent samples t-test
also type of wilcoxon test
When is Mann Whitney U test used?
for between subjects design
ordinal data
or interval / ratio data that is skewed
Why do the tests work with skewed data?
because it changes raw data into ranks
What is another popular effect size other than Cohen’s d?
Vargha-Delaney’s A
What does Vargha-Delaney’s A do?
tells us how often, on average, which condition outperforms another
A measure is a value between 0 and 1
What does it mean if the A measure is exactly 0.5?
then 2 techniques achieve equal performance
What does it mean if A measure is less than 0.5?
then 1st condition has lower values
What does it mean if A measure is more than 0.5?
2nd condition had lower values
The farther the A measure is from 0.5 the…
larger the difference
What is the Wilcoxon signed rank test?
A non-parametric version of paired samples t-test
When is Wilcoxon signed rank test used?
within subjects design
for ordinal data
or interval /ratio data that’s skewed
How do you rank data?
scores are ordered from lowest other highest
lowest value given rank of 1
second lowest rank given rank of 2 etc.
What do you do if you have tied ranks?
what the rank would be (if numbers were different) are added together
then divided by how many values are the same
next value (which is different) is ranked as normal
