Non Parametric Tests

Question 1

What are assumptions for parametric tests?

Answer 1

1.the data are normally distributed
2.the groups that are being compared have similar variance
3.the data are independent

Question 2

When to use non parametric tests?

Answer 2

If your data does not meet these assumptions you might still be able to use a nonparametric statistical test, which have fewer requirements but also make weaker
inferences.

One independent variable (factor), two conditions (levels)

Question 3

What are within-subject and between-subject non parametric tests

Answer 3

Within-subjects
* Sign Test
* Wilcoxon Matched-Pairs test

Between-subjects
* Wilcoxon Rank-Sum test (or Mann-Whitney U test)

Question 4

What are assumptions for the sign test?

Answer 4

• Assumptions/ requirements:
• Ordinal/scale data
• Paired/Matched samples
• Can test hypotheses about differences between the mean/median

Question 5

Example write up of the sign test

Answer 5

Prior to the statistics class mean enjoyment of statistics was 4.67 whereas afterwards it was 6.33.

A sign test was conducted to compare the
before and after enjoyment scores with
the test revealing that 13 of the 15 students exhibited positive differences, p = .003 .

The results suggest that the implementation of a statistic class can
increase overall student enjoyment of
statistics.

Question 6

Limitations of the sign test

Answer 6

• The magnitude of the change is completely ignored –> Lacks
  power (i.e. the ability of a test to detect an effect of a particular
  size)
• Ignores size of difference
• Ignores tied scores
• Only assesses two conditions

Question 7

How to write up the Wilcoxon test

Answer 7

Prior to the statistics class mean enjoyment of statistics was 4.67
whereas afterwards it was 6.33.

A Wilcoxon matched-pairs test was conducted to compare the before and after enjoyment scores with the test revealing that 13 of the 15 students exhibited positive differences, z = -3, p = .003.

The results suggest that the implementation of a statistic class
can increase overall student enjoyment of statistics

Question 8

Overview of the seminar

Answer 8

• Why and when do we use non-parametric tests?
• How do we conduct and interpret a sign test?
• How do we conduct and interpret a Wilcoxon Matched
  Pairs?
• How do we conduct and interpret a Wilcoxon
  rank-sum/Mann-Whitney?