Lecture 9

Question 1

What are the 2 types of non-parametric correlation methods?

Answer 1

• Spearmans rank

- Kendalls tau

Question 2

What is the method of a spearmans rank correlation?

Answer 2

Step 1: Rank transformation of x and y
Step 2: Pearsons r correlation on the transformed variables
Step 3: Produces a correlation coefficent: P

Question 3

What data (normal/ non-normal) can spearmans be used for?

Answer 3

Both

Question 4

What type of relationship does spearmans measure?

Answer 4

Monotonic

Question 5

What data (normal/ non-normal) can Pearsons be used for?

Answer 5

Just Normal

Question 6

What type of relationship does Pearsons measure?

Answer 6

Linear relationships

Question 7

What is the method for Kendalls Tau

Answer 7

Step 1: Rank transform variables
Step 2: count concordant and discordant pairs
Step 3: Correlation coefficient denoted by greek letter tau (T)

Question 8

What does the Tau-A correction do to ties?

Answer 8

No adjustment for ties, just keeps it in range -1 to +1

Question 9

What does the Tau-B correction do to ties?

Answer 9

Adjusts ties to keep range -1 to +1. The most common. Easy to interpret

Question 10

Do Spearmans and Kendalls yield similar results?

Answer 10

Yes typically similar results

Question 11

what are the advantages of Kendall’s Tau?

Answer 11

√ More robust for significance testing in smaller sampels

√ Particularly suitable for discrete + Ordinal data

Question 12

Evaluate ranked group difference tests

Answer 12

√ Ranking method provides robustness against outliers
√ Doesnt require normally distributed data
√ Can use with ordinal, unlike t -test
X - has less power than t tests

Question 13

What are the 3 non-parametric tests for group differences?

Answer 13

Binomial test, Mann-Whitney u-test, Wilcoxon signed-rank test

Question 14

When would you use binomial test?

Answer 14

With binomial data

Question 15

How to you calculate correlation tests in SPSS?

Answer 15

Analyse - correlate - Bivariate - add variables - select method (Pearson, spearmans, kendalls)

Question 16

What is the method for wilcoxon?

Answer 16

Step 1: Work out the difference between a pairt and allocate it a sign (+/-)
Step 2: rank them by differnce and multiply rank with sign
Step 3: Sum of signed ranks gives the value ‘W’
Step 4: The W and DF and used to derive the ‘Z statistic’ and significance ‘p’
- SPSS does all this

Question 17

When would you use Wilcoxon?

Answer 17

Repeated measures design (its an alternative to the related t-test)

Question 18

When would you use Mann Whitney?

Answer 18

For indepedent groups

Question 19

What is the method for Mann whitney

Answer 19

Step 1: Combine all samples and rank all values
Step 2: Add up ranks which came from each sample, to find sum of ranks for each sample
Step 3: This gives you a ‘u’ value
Step 4: u and df used to derive z, which is used to get p

Question 20

What can the ‘u’ value from the mann whitney test range from?

Answer 20

0 (complete seperation between groups)
to
n1 X n2 (no seperation between them - accept null)

Question 21

How do you calculate Wilcoxon in SPSS?

Answer 21

Analyse - non parametric tests - legacy dialogues - 2 related samples - enter variables - select wilcoxon

Question 22

How do you calculate Mann whitney in SPSS?

Answer 22

Analyse - non parametric tests - legacy dialogues - 2 independent samples - enter variables - select mann whitney