 Mar 2023

journals.plos.org journals.plos.org

Nonparametric statistics are often preferred to parametric tests when the sample size is small and the data are skewed or contain outliers.


scholarworks.umass.edu scholarworks.umass.edu

Noteworthy for its longstanding influence is thebook “Nonparametric statistics for the behavioralsciences” by Siege
Highly cited book from 1956!
Siegel (1956) pointed out that traditional parametric tests should not be used with extremely small samples, because these tests have several strong assumptions underlying their use. The ttest requires that observations are drawn from a normally distributed population and the twosample ttest requires that the two populations have the same variance. According to Siegel (1956), these assumptions cannot be tested when the sample size is small. Siegel (1957) stated that “if samples as small as 6 are used, there is no alternative to using a nonparametric statistical test unless the nature of the population distribution is known exactly” (p. 18).

 Nov 2020

statistics.laerd.com statistics.laerd.com

Assumption #4:
When to choose between the KruskallWallis mean ranks and the median test.

 Mar 2019

statistics.laerd.com statistics.laerd.com

From this data, it can be concluded that cholesterol concentration in the diet group was statistically significantly higher than the exercise group (U = 110, p = .014). Depending on the size of your groups, SPSS Statistics will produce both exact and asymptotic statistical significance levels. Understanding which one to use is explained in our enhanced guide.
Phrasing results for the MannWhitney Utest.
