Year	Number of
1990	0.31
1991	0.33
1992	0.35
1993	0.37
1994	0.39
1995	0.41
1996	0.43
1997	0.44
1998	0.45
1999	0.46
2000	0.48
2001	0.48
2002	0.55
2003	0.6
2004	0.65
2005	0.67
2006	0.69
2007	0.71
2008	0.72
2009	0.76
2010	0.76
2011	0.8
2012	0.83
2013	0.86
2014	0.89
2015	0.92
2016	0.94