Year	Percent
1979	0.106
1990	3.5
1991	5.1
1992	7.3
1993	10.1
1994	13.3
1995	16.6
1996	19.7
1997	22.2
1998	24.1
1999	25.3
2000	26
2001	26.3
2002	26.3
2003	26.1
2004	25.8
2005	25.5
2006	25.3
2007	25.1
2008	24.9
2009	24.1
2010	23.7
2011	23.4