L11 - Inferential Analysis - Spearman’s Rho, Mann Whitney, Chi Squared & Wilcoxon (Non-Parametric Tests)

Question 1

What are critical values?

Answer 1

• A critical value is a numerical value you find in the statistical tables in the appendix that helps to determine the significance of your results
• can determine whether your results are significant or not e.g. is there a real difference between two conditions (if yes, then the results are significant and the experimental hypothesis should be accepted), or is the difference due to fluke or chance (if this is true, then we accept the null hypothesis).

Question 2

Spearman’s Rho

Answer 2

• This is used when we wish to test a relationship or correlation between two variables.
• The data should be ordinal (at least).
• The data are in related pairs This is a non-parametric test
• Spearman’s Rho calculates the strength of the relationship between the two variables e.g. if r is -1.0 this means there is a perfect negative correlation between two variables, and if r is +1.0 then this is a perfect positive correlation.

Question 3

What does ‘N’ stand for

Answer 3

Number of participants

Question 4

What does ‘d’ stand for?

Answer 4

Difference between rank A&B worked out by Rank A - Rank B

Question 5

Mann Whitney

Answer 5

• This test is used when we are looking for a test of difference
• This statistical test is used when we have an independent group design.
• We also use this test when we have data that is ordinal (can be placed in rank order) or interval.
• This test is a non-parametric test

Question 6

What does ‘Na’ Stand for

Answer 6

• number of participants in smaller sample

Question 7

What does ‘Nb’ stand for

Answer 7

Number of participants in larger sample

Question 8

What does ‘T’ stand for?

Answer 8

Sum of ranks in smaller sample

Question 9

Chi squared

Answer 9

• This test can be used for either a test of association or for a test of difference (that is why this is a special statistical test).
• We use chi squared (for a test of difference) when we have an independent measures design and are using nominal data in the form of frequencies or separate categories.
  • We would also use chi squared if we are testing an association that might occur between two variables. Again, the data would be nominal and would use an independent measures design
  • Chi squared is a non-parametric test

Question 10

What are degrees of freedom?

Answer 10

• corresponds to number of values that are free to vary
  (No. of rows 1) x (No. of columns 1) = degrees of freedom

Question 11

Wilcoxon

Answer 11

• used to measure test of difference
• used when repeated measures/matched participants
• ordinal data
• non-parametric test

Question 12

To work out Wilcoxon matched pair design results you should….

Answer 12

• calculate sum of positive ranks
• then negative ranks
• ‘t’ is smaller value of+ve/-ve ranks
• ‘n’ is no. of ppt that scored differently in each condition