@book{9128,
	author = {Snijders, T. A. B. and Bosker, R. J.},
	title = {Multilevel analysis :},
	publisher = {Sage Publications,},
	year = {1999.},
	address = {London ;},
	url = {http://www.loc.gov/catdir/enhancements/fy0656/99075734-d.html}
}