Year	Percent
1990	0.32
1991	0.33
1992	0.35
1993	0.37
1994	0.39
1995	0.41
1996	0.44
1997	0.45
1998	0.48
1999	0.51
2000	0.52
2001	0.55
2002	0.56
2003	0.58
2004	0.59
2005	0.61
2006	0.62
2007	0.64
2008	0.64
2009	0.67
2010	0.7
2011	0.7
2012	0.73
2013	0.74
2014	0.77
2015	0.78