Year	Number of
1990	0.44
1991	0.45
1992	0.47
1993	0.49
1994	0.51
1995	0.53
1996	0.54
1997	0.55
1998	0.57
1999	0.58
2000	0.56
2001	0.56
2002	0.56
2003	0.57
2004	0.59
2005	0.62
2006	0.64
2007	0.66
2008	0.67
2009	0.7
2010	0.71
2011	0.74
2012	0.77
2013	0.79
2014	0.82
2015	0.85
2016	0.86