Year	Percent
1979	0.01
1990	4.8
1991	5.7
1992	6.5
1993	7.1
1994	7.6
1995	7.8
1996	7.9
1997	7.9
1998	7.7
1999	7.5
2000	7.3
2001	7.1
2002	6.8
2003	6.6
2004	6.4
2005	6.2
2006	6
2007	5.9
2008	5.8
2009	5.8
2010	5.8
2011	5.8