@book{20506,
	author = {Dougherty, Christopher},
	title = {Introduction to econometrics },
	publisher = {Oxford University Press,},
	year = {2002.},
	address = {Oxford },
	edition = {2nd ed.},
	url = {http://www.loc.gov/catdir/enhancements/fy0613/2002279904-d.html}
}