Year	Percent
1990	0.7
1991	0.7
1992	0.69
1993	0.69
1994	0.69
1995	0.68
1996	0.68
1997	0.67
1998	0.67
1999	0.67
2000	0.66
2001	0.66
2002	0.66
2003	0.65
2004	0.65
2005	0.64
2006	0.68
2007	0.71
2008	0.74
2009	0.77
2010	0.81
2011	0.81
2012	0.81
2013	0.81
2014	0.82
2015	0.82