nonparametric tests
Last reviewed 01/2018
Features of nonparametric statistical methods include:
- nonparametric statistical tests can be used when the data being analysed is not a normal distribution
- many nonparametric methods do not use the raw data and instead use the rank order of data for analysis
- nonparametric methods can be used with small samples
- two
commonly used nonparametric methods are:
- the Mann-Whitney U test
- this is the nonparametric equivalent of the unpaired t-test
- applied when there are two independent samples
- the Wilcoxon matched-pairs signed
ranks test
- equivalent to the paired t-test
- both of these tests have a power-efficiency of 95.5% when compared to their parametric equivalents (this means that the equivalent parametric test would be just as effective with a sample size that is 4.5% smaller than used in the nonparametric tests). The power-efficiency illustrates the fact that if all conditions of normality (of the sample distribution) are met, then nonparametric methods waste data
- the Mann-Whitney U test
Reference:
- Doctor (March 22nd 2005):33-5.