@article {pmid2085632,
	title = {Assessing proportionality in the proportional odds model for ordinal logistic regression},
	journal = {Biometrics},
	volume = {46},
	number = {4},
	year = {1990},
	month = {Dec},
	pages = {1171{\textendash}1178},
	author = {Brant, R.}
}
