For categorical data, there is no mean or median, and so the measures of variation described in Measures of Variability can’t be used. Instead, we use a measure of the distribution of observations among the categories.
Topics
References
Offwell Woodland & Wildlife Trust (2016) Simpson’s diversity index. Ecological sampling methods
http://www.countrysideinfo.co.uk/simpsons.htm
Krebs, C. J. (2014) Species diversity measures
https://www.zoology.ubc.ca/~krebs/downloads/krebs_chapter_13_2017.pdf
Wikipedia (2016) Diversity index
https://en.wikipedia.org/wiki/