Year	Percent
1979	0.01
1990	10.2
1991	10.7
1992	10.5
1993	10.2
1994	9.8
1995	9.3
1996	8.8
1997	8.4
1998	8
1999	7.6
2000	7.3
2001	7
2002	6.8
2003	6.6
2004	6.4
2005	6.4
2006	6.3
2007	6.3
2008	6.4
2009	6.9
2010	7
2011	7.2