Equality of medians (non-parametric) Flashcards
T-tests rely on the variables being….
Symmetrical/normally distributed
What is the non-parametric analogue of the one sample t-test?
The Wilcoxon Signed Rank Test
When should you used the Wilcoxon Signed Rank Test?
▪️Compare median to a pre-specified value
▪️Skewed continuous data
▪️Ordinal (interval) or discrete data
What is the null hypothesis of a Wilcoxon Signed Rank Test?
The MEDIAN equals a certain predefined value
What assumptions are needed for the Wilcoxon Signed Rank Test?
▪️Observations are randomly and independently drawn
▪️At least interval data (more than 5 categories unless you can assume distances are equidistant)
What statistics do your report for the Wilcoxon Signed Rank Test?
The standardised test statistic (Z) and the p value
What is the non-parametric analogue of the independent sample t-test?
Mann-Whitney U test
When would you use the Mann-Whitney U test?
▪️Compare distributions of two different samples
▪️Skewed continuous data
▪️Ordinal (interval) or discrete data
What is the null hypothesis of a Mann-Whitney U test?
The two DISTRIBUTIONS are equal
What assumptions are needed for the Mann-Whitney U test?
▪️Observations are randomly and independently drawn
▪️At least interval data (more than 5 categories unless you can assume distances are equidistant)
What statistics do you report for the Mann-Whitney U test?
The Mann-Whitney U number and the p-value
(and describe how they differ)
What is the non-parametric analogue of the paired sample t-test?
Wilcoxon Matched-Pair Signed Rank Test
When would you use the Wilcoxon Matched-Pair Signed Rank Test?
▪️Compare medians of two paired or matched groups
▪️Skewed continuous data
▪️Ordinal (interval) or discrete data
What assumptions are needed for the Wilcoxon Matched Pair Signed Rank Test?
▪️Observations are randomly and independently drawn
▪️At least interval data (more than 5 categories unless you can assume distances are equidistant)
▪️Two samples need to be dependent observations of the cases (paired or matched)
What statistics do you report for your Wilcoxon Matched Pair Signed Rank Test?
The standardised test statistic (Wilcoxon rank sum Z) and the p-value
