@book{207464,
	author = {Hackshaw, Allan K.,},
	title = {A concise guide to observational studies in healthcare /},
	publisher = {John Wiley & Sons Inc. :},
	year = {2015.},
	address = {Chichester, West Sussex, UK ;},
	url = {http://onlinelibrary.wiley.com/book/10.1002/9781118527122}
}