Section 8 (Pgs 94-108) Flashcards
Basically, when are non-parametric methods used?
When the variables are not normally dsitributed
When the data is skewed
What do non-parametric methods use instead of the actual values of the data?
Ranks of the data
Are non-parametric methods more or less powerful than parametric methods?
Why?
Less powerful
They do not utilise all the data
What 3 variables are most likely to warrant the use of non-parametric methods?
Counts
Ranks
Scores
What can sometimes achieve normality for counts, ranks and scores?
Square root transformation
What should you always do before deciding on non-parametric methods?
Explore methods of transforming the data
What should you look at to determine whether data is normally distributed?
Normal plot
Box-and-whisker diagram
Shaprio-Wilk statistic
Coefficient of skewness
What is the most appropriate measure of centre in normally distributed data?
Mean
Is not normally distributed data normally symmetrically or non-symmetrically distributed?
Non-symmetrically (skewed)
What is the most appropriate measure of centrality in non-normally distributed data?
Median
When is non-parametric tests of the average of a single sample indicated?
Data is not plausibly normal (normal plot, box-and-whisker plot, shapiro-wilk statistic, coefficient of skewness)
Transformations to address the problem cannot be found
Sample size is small?
What 2 non-parametric procedures can be used to test hypothesis about the median of a single sample?
Sign test
Wilcoxon signed rank sum test
What principle is the sign test based on?
The numbers of observations above and below the hypothesised median
If the null hypothesis is true, these should be equal
Which out of the sign test and the wilcoxon signed rank sum test is preferable?
Why?
Wilcoxon signed rank sum test
Based on ranks and therefore incorporates some measure of the actual values
Why is the sign test sometimes used instead of the wilcoxon signed rank sum test?
Data must be approximately symmetrically distributed for the wilcoxon signed rank sum test