L11- Inferential Analysis – Spearman’s Rho, Mann Whitney, Chi Squared and Wilcoxon – (Non Parametric tests)

Question 1

What is the critical value?

Answer 1

In a statistical test you will compare your final result with a critical value (numerical value found in statistical tables- helps determine significance of results)

• If significant (real difference between 2 conditions exists, then accept experimental hypothesis
• BUT if not significant (due to fluke or chance) accept null hypothesis

Question 2

When writing your answer regarding the significance of results once a particular statistical test has been conducted, what are the key points/stages to always remember?

Answer 2

1) Justify choice of statistical test (refer to whether test of difference, correlation or association, design used and level of measurement used
2) Calculate results of statistical test
3) Compare results to critical value (decide on significance)
4) Mention level of significance selected e.g. p<0.05 (5%) and whether hypothesis 1 tailed or 2 tailed
5) … accepted or rejected experimental and null hypothesis

Question 5

What does spearman’s rho calculate?

Answer 5

Calculates strength of relationship between the 2 co-variables
e.g. if r is -1.0 = perfect ➖ correlation between 2 variables
if r is +1.0 then this is a perfect ➕ correlation

Question 6

For a spearman’s rho’s test what should the relationship between the calculated and critical value be for the results to be significant?

Answer 6

Calculated value must be greater than or equal to critical value

Question 7

What does ‘n’ stand for in spearman’s rho?

Answer 7

Number of pps

Question 8

What does ‘d’ stand for in spearman’s rho?

Answer 8

Difference

Question 9

What does ‘Na’ start for in Mann Whitney U test?

Answer 9

Number of pps in the smaller sample

Question 10

What does ‘Nb’ stand for in Mann Whitney U test?

Answer 10

Number of pps in the larger sample

Question 11

What does ‘T’ stand for in Mann Whitney U test?

Answer 11

Sum of the ranks in the smaller sample

Question 12

For a Chi Squared test what should the relationship between the calculated and critical value be for the results to be significant?

Answer 12

Calculated value must be greater or equal to the critical value

Question 13

What does ‘observed value’ mean for in a Chi Squared test?

Answer 13

Calculated value- numerical value calculated when using statistical test- compared with critical value to determine significance

Question 14

What does ‘degrees of freedom’ mean for in a Chi Squared test?

Answer 14

Number of values that are free to vary
(Number of rows with actual values in them) multiplied by (number of columns with actual values in them) = degree of freedom

Question 16

What are the steps involved in carrying out a Wilcoxon test?

Answer 16

1) Calculate the sum of ➕ ranks

2) Calculate the sum of ➖ ranks

Question 17

What does ‘T’ mean for in a Wilcoxon signed ranks test?

Answer 17

Smaller value

Question 18

What must you remember if you encounter a negative calculated value?

Answer 18

Ignore the ➖ when comparing the calculated value to the critical value but include the ➖ when writing out your final answer (even though it might not make sense).

Question 19

What does ‘N’ mean for in a Wilcoxon signed ranks test?

Answer 19

Number of pps

Question 21

For a Wilcoxon signed ranks test what should the relationship between the calculated and critical value be for the results to be significant?

Answer 21

Calculated value must be less than or equal to the critical value

Question 22

For a Mann Whitney U test what should the relationship between the calculated and critical value be for the results to be significant?

Answer 22

Calculated value must be less than or equal to critical value