Year	Percent
1979	0.01
1990	5.2
1991	5.2
1992	5
1993	4.8
1994	4.6
1995	4.4
1996	4.3
1997	4.1
1998	4
1999	3.9
2000	3.9
2001	3.8
2002	3.8
2003	3.7
2004	3.7
2005	3.6
2006	3.6
2007	3.5
2008	3.5
2009	3.3
2010	3.3
2011	3.3