Flashcards in Non parametric methods Deck (13)

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1

## What is a non parametric form of a two-sample t-test?

### Mann-Whitney test

2

## How does a Mann-whitney test work?

### If the two samples are drawn from the same population, we would expect to receive a random sample of the ranks and therefore the sum of the ranks would be approximately equal

3

## What are the technicalities of a Mann whitney test?

###
assumes that the data can be uniquely ranked

Ho is that both groups' observations been sampled from the same distribution

Less powerful than a two-sample t-test. This difference is usually only noticed in small samples

4

## What is done in the case of tied observations?

### give tied observations the average of the ranks that would have been used for them if the values were different

5

## What are the assumptions for calculating the confidence intervals of the medians in Mann whitney tests?

###
the distributions have the same shape

The distributions only vary by their medians not their variability

these are very similar to the assumptions for parametric tests and sometimes it would be more appropriate to use these

6

## Give an example of the non-parametric version of a one-sample t-test

### Wilcoxon signed ranks rest

7

## Describe the wilcoxon signed rank test

### ranks are calculated based on the differences between the observations and the target value

8

## Notes on the wilcoxon signed rank test

###
holds only when the differences are non zero

assumes the observations come from a population with a symmetrical distribution - usually only if data is normal . if it doesn't use a sign test- much lower power

It is possible to calculate confidence intervals for the median

9

## Describe the WIlcoxon matched pairs test

###
when there are two measurements of the same quantity o each individual in a single sample

Ho- values of first measurement are approximately equal to the measurement of he second measurement

calculate the difference between each individual pair of measurements, then carry out test based on ranks of the within pair differences

10

## Notes on Wilcoxon matched pairs test

###
effectively Wilcoxon signed rank test

only holds when differences are non-zero

assume from a symmetrical distribution

11

## What is the name of a method for non-parametic analysis of variance ?

### The Krushal-Wallis test

12

## Describe the Krushal-Wallis test

###
mathematical extension of the Mann whitney test

Ho- different groups come from populations with the same distribution

Use bonferroni to account for multiple testing

13