Wilcoxon signed ranks test Flashcards
When is this test used?
Repeated measures design / matched participants design
Ordinal level data
How to remember what test to use
ORW
Ogre Railed Whale
Ordinal level data
Repeated measures
Wilcoxon signed ranks
Difference in scores between control condition and experimental condition
Take away experimental condition score from experimental condition score to find difference
What is done to participants who had no change in score from experiment to control?
Ignore score
Ranking differences between conditions
Give smallest difference the smallest rank and work way up to biggest difference
What happens if the difference is the same?
Give the midpoint rank to these differences and cross off the ranks used up
Is the positive or negative sign taken into account with ranking?
no
How to find calculated value of T
Add together the ranks of the least frequent sign, eg the ranks of all positive or all negative differences
Critical value of T
Found from two tailed hypothesis at p<0.05
And n = number of participants who showed a difference
N
Number of participants who showed a difference
Is n equal to number of participants in the study?
No because some participants might not show a difference so are discounted
ONLY PARTICIPANTS WHO SHOWED A DIFFERENCE
How do we know the results are due to chance? (and not statistically different)
Because the calculated value is bigger than the critical value
How do we know the results are not due to chance? (and statistically different)
Because the calculated value is smaller than the critical value
