Year	Percent
1981	0.01421
1990	0.7
1991	1.2
1992	1.8
1993	2.9
1994	4.3
1995	6.1
1996	8.4
1997	10.7
1998	12.9
1999	14.8
2000	16.1
2001	17.1
2002	17.7
2003	18
2004	18.1
2005	18.1
2006	18.1
2007	18
2008	17.9
2009	17.2
2010	17.3
2011	17.3