@book{31,
	author = {Gujarati, Damodar N. and Porter, Dawn C.},
	title = {Basic econometrics /},
	publisher = {McGraw-Hill Irwin,},
	year = {c2009.},
	address = {Boston :},
	edition = {5th ed.},
	url = {http://www.loc.gov/catdir/toc/ecip0825/2008035934.html}
}