# Non-Parametric Models - From Textbook Flashcards

What are the 4 most common non-parametric procedures?

Mann-Whitney test

Wilcoxon signed-rank test

Friedman’s test

Kruskal-Wallis test

What do the 4 most common non-parametric procedures overcome?

Distributional problems

How do the 4 most common non-parametric procedures overcome distributional problems?

By ranking the data

The model is then fitted to the ranks and NOT the raw scores.

Why are the 4 most common non-parametric procedures fitted to the ranks and NOT the raw scores?

To eliminate the effect of outliers + irons out problems w/ skew.

i.e you have 20 data points + the 2 highest are 30 and 60, the scores become ranks of 19 + 20.

-ive to non-parametric tests when fitting the mode to ranks and NOT the raw scores

Lose info about magnitude of differences between scores

What is meant by statistical power?

Ability of a test to find an effect that genuinely exists.

If there’s a genuine effects = non-parametric test is less likely to detect it than a parametric one.

What do you do on SPSS when comparing groups containing different entities

Select analyse

Non-parametric tests

Independent samples

What do you do on SPSS when comparing scores that were taken from the same entities under difference conditions

Select analyse

Non-parametric tests

Related samples

SPSS NON-PARAMETRIC TESTS

What do you select in objectives tab

Customise analysis

What are the options to compare the distribution in 2 conditions containing scores from different entities?

Mann-Whitney test

Wilcoxon rank-sum test

Rank data - ignoring the group to which a person belonged - from lowest to highest.

What should you do if there’s no difference between the groups?

Find a similar no. of high + low ranks in each groups.

If you added up the ranks, you would expect summed total of ranks in each group to be ~ same.

When groups have unequal no. of participants in them.

What is the Test statistic (Ws) for the Wilcoxon rank-sum test?

Sum of ranks in the group containing the fewer people

When group sizes are equal its the value of the smaller summed rank.

How to run a Mann-Whitney test using SPSS

Select analyse

Non-parametric tests

Independent samples

Fields tab

Custom field assignments

Specify model by dragging variables into test fields

Calculation for effect size

r = z score / (square root of size of study)

What must you write for the results from the Mann-Whitney test

Test statistic + its significance