Year	Number of
1990	0.54
1991	0.56
1992	0.58
1993	0.61
1994	0.63
1995	0.66
1996	0.69
1997	0.71
1998	0.72
1999	0.74
2000	0.76
2001	0.76
2002	0.77
2003	0.77
2004	0.78
2005	0.79
2006	0.79
2007	0.79
2008	0.79
2009	0.8
2010	0.82
2011	0.82
2012	0.84
2013	0.85
2014	0.86
2015	0.87
2016	0.88