Year	Percent
1979	0.01
1990	12.7
1991	13.6
1992	14.2
1993	14.6
1994	14.9
1995	15
1996	14.9
1997	14.8
1998	14.7
1999	14.6
2000	14.4
2001	14.3
2002	14.2
2003	14.1
2004	14
2005	13.9
2006	13.8
2007	13.7
2008	13.6
2009	12.9
2010	12.7
2011	12.5