L5 - Wilcoxon Signed-Rank Test

Question 1

What is the purpose of the Wilcoxon signed-rank test?

Answer 1

Compares differences between 2 treatments for the same group
Ranks the difference between each pair of scores (ignores sign)

Question 2

What assumptions need to be in place to carry out a Wilcoxon test?

Answer 2

Data is paired + ordinal

Question 3

What is H0 for wilcoxon tests?

Answer 3

No difference in treatments

Question 4

What is H1 for wilcoxon tests?

Answer 4

Significant difference in treatments

Question 5

How do you calculate wilcoxon tests?

Answer 5

1. Subtract: Calculate the difference
   between scores for each
   treatment.
2. Absolute Difference: Find the
   absolute values of differences.
3. Rank Scores: Rank these absolute
   differences.
   * Exclude zero differences from
   ranking.
   * For tied ranks, assign the average
   rank.
4. Re-allocate Signs: Re-assign the
   original signs (+ or -) to the ranks.
5. Sum Ranks: Calculate the sum of
   ranks for positive and negative
   differences.
6. Determine Significance: Use a lookup table to find if the summed ranks indicate a significant difference.