Year	Number of
1990	0.42
1991	0.44
1992	0.46
1993	0.47
1994	0.49
1995	0.5
1996	0.52
1997	0.53
1998	0.54
1999	0.56
2000	0.58
2001	0.6
2002	0.62
2003	0.65
2004	0.68
2005	0.71
2006	0.73
2007	0.75
2008	0.77
2009	0.79
2010	0.82
2011	0.83
2012	0.85
2013	0.87
2014	0.89
2015	0.91
2016	0.95