@book{75484,
	author = {Goertz, Gary},
	title = {Social science concepts  a user's guide},
	publisher = {Princeton University Press},
	year = {2006},
	address = {Princeton (Nueva Jersey, Estados Unidos)},
	url = {http://www.loc.gov/catdir/enhancements/fy0654/2005043930-t.html}
}