16.1 Compositional data
https://en.wikipedia.org/wiki/Categorical_distribution https://en.wikipedia.org/wiki/Dirichlet_distribution https://en.wikipedia.org/wiki/Dirichlet-multinomial_distribution https://en.wikipedia.org/wiki/Compositional_data https://www.annualreviews.org/content/journals/10.1146/annurev-statistics-042720-124436 https://www.geo.fu-berlin.de/en/v/soga-r/Advances-statistics/Feature-scales/Intro_compositional_data/index.html