L8: Non parametric tests Part 1

Question 1

What are the assumptions for parametric tests?

Answer 1

• samples drawn from normally distributed populations

- variances are the same

Question 2

When are non parametric tests used?

Answer 2

Used when assumptions for parametric tests are not met.

Question 3

What are the advantages of non parametric tests?

Answer 3

• no restrictive assumptions
• uses ranks rather than actual values –> can be performed relatively quickly for small samples and less sensitive to measurement error and outliers

Question 4

What are the disadvantages of non parametric tests?

Answer 4

• less powerful than parametric tests, if the assumptions underlying parametric tests are satisfied –> require larger sample size if same statistical power is needed.

Question 5

What test to use to compare data between two independent groups with continuous non-normally distributed data or ordinal data presented as median (IQR)?

Answer 5

Wilcoxon rank sum test (Mann-Whitney U test)

Question 6

What is the null and alternative hypotheses for the wilcoxon rank sum test?

Answer 6

H0: There is no difference between the medians of the two underlying populations
H1: depends on qn