Research Methods Y2 - Mann Whitney/Wilcoxon

Question 1

What is the purpose of the Mann–Whitney test?

Answer 1

The Mann–Whitney test is used to look for a difference between two groups of scores. It is appropriate when the data is ordinal (scores are ranks) or interval but not normally distributed.

Question 2

What are the hypotheses in the Mann–Whitney test example?

Answer 2

Alternative hypothesis: There is a difference in ratings for ‘suitability of an interview’ based on whether a job applicant is described as having been diagnosed with schizophrenia (Group A) or not (Group B).

Null hypothesis: There is no difference in ratings for ‘suitability of an interview’ based on whether a job applicant is described as having been diagnosed with schizophrenia (Group A or not Group B).

Question 3

What is the first step in the Mann–Whitney test?

Answer 3

Calculate the rank of scores. Combine scores from both groups into one data set, rank them, and then calculate the sum of ranks for each group.

Question 4

How is U calculated in the Mann–Whitney test?

Answer 4

U = Ra - (Na(Na+1))/2 Where Ra is the sum of the ranks and Na is the number of pp

Question 9

What is the critical value in the Mann–Whitney test?

Answer 9

The critical value of
𝑈
U is found using a critical values table. For a two-tailed test at 𝑝≤0.05
p≤0.05, the critical value depends on 𝑛1and 𝑛2.

Question 10

How do you determine significance in the Mann–Whitney test?

Answer 10

If the calculated U is equal to or less than the critical value, the null hypothesis is rejected, and the alternative hypothesis is accepted.

Question 11

What is the purpose of the Wilcoxon test?

Answer 11

The Wilcoxon test is used to investigate differences in scores in repeated measures designs, comparing scores from the same participants before and after treatment.

Question 12

What are the hypotheses in the Wilcoxon test example?

Answer 12

Alternative hypothesis: There is a difference in young offenders’ scores on an anger questionnaire before and after treatment.
Null hypothesis: There is no difference in young offenders’ scores on an anger questionnaire before and after treatment.

Question 13

What is the first step in the Wilcoxon test?

Answer 13

Calculate the difference between the two sets of data. Rank the absolute differences, ignoring signs.

Question 14

How is the T value calculated in the Wilcoxon test?

Answer 14

T is the sum of the ranks of the less frequent sign (either positive or negative).

Question 15

How do you determine significance in the Wilcoxon test?

Answer 15

If the calculated T is less than or equal to the critical value, the null hypothesis is rejected, and the alternative hypothesis is accepted.

Question 16

What is an ‘Inferential test’?

Answer 16

An inferential test is a statistical test used to determine whether two samples are significantly different.

Question 17

What does ‘Ordinal data’ mean?

Answer 17

Ordinal data refers to data that is ranked or ordered but does not have equal intervals between points.

Question 18

What does ‘Significant difference’ mean?

Answer 18

A significant difference indicates that the results are unlikely to be due to chance, typically at 𝑝≤0.05.

Question 19

What is a ‘Two-tailed test’?

Answer 19

A two-tailed test is used when the alternative hypothesis predicts a difference but does not specify the direction of the difference.