Year	Percent
1979	0.07
1990	3.9
1991	5.4
1992	7
1993	8.4
1994	9.6
1995	10.3
1996	10.5
1997	10.5
1998	10.1
1999	9.6
2000	9
2001	8.4
2002	7.9
2003	7.5
2004	7.1
2005	6.8
2006	6.6
2007	6.4
2008	6.3
2009	6.2
2010	6.2
2011	6.2