https://www.jstor.org/stable/25502206?seq=1
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4221103/
https://academic.oup.com/ije/article/44/1/324/654595
https://academic.oup.com/biostatistics/article/9/4/750/259081 (also has ordinal)