Year	Percent
1990	0.56
1991	0.41
1992	0.36
1993	0.35
1994	0.36
1995	0.38
1996	0.4
1997	0.41
1998	0.43
1999	0.43
2000	0.43
2001	0.43
2002	0.41
2003	0.4
2004	0.38
2005	0.34
2006	0.31
2007	0.3
2008	0.3
2009	0.28