@book{77051,
	author = {Dunning, Thad},
	title = {Natural experiments in the social sciences :},
	publisher = {Cambridge University Press,},
	year = {2012},
	series = {Strategies for social inquiry},
	address = {Cambridge :},
	url = {http://www.loc.gov/catdir/enhancements/fy1210/2012009061-t.html}
}