Year	Percent
1979	0.113
1990	3.1
1991	4.6
1992	6.3
1993	7.9
1994	9
1995	9.7
1996	10.1
1997	10.1
1998	10
1999	9.8
2000	9.4
2001	8.9
2002	8.4
2003	7.8
2004	7.2
2005	6.6
2006	6.1
2007	5.5
2008	5.1
2009	5.1
2010	4.9
2011	4.6