Year	Percent
1990	0.21
1991	0.29
1992	0.37
1993	0.46
1994	0.53
1995	0.58
1996	0.6
1997	0.58
1998	0.56
1999	0.53
2000	0.47
2001	0.42
2002	0.4
2003	0.37
2004	0.35
2005	0.35
2006	0.38
2007	0.39
2008	0.39
2009	0.41
2010	0.42
2011	0.36