Year	Percent
1979	0.01
1990	3.9
1991	4
1992	3.9
1993	3.8
1994	3.6
1995	3.4
1996	3.2
1997	2.9
1998	2.7
1999	2.5
2000	2.3
2001	2.1
2002	1.9
2003	1.7
2004	1.6
2005	1.5
2006	1.4
2007	1.3
2008	1.2
2009	1.2
2010	1.2
2011	1.1