Year	Number of
1990	0.49
1991	0.51
1992	0.53
1993	0.55
1994	0.57
1995	0.59
1996	0.61
1997	0.62
1998	0.64
1999	0.66
2000	0.68
2001	0.68
2002	0.69
2003	0.69
2004	0.7
2005	0.7
2006	0.7
2007	0.71
2008	0.71
2009	0.72
2010	0.72
2011	0.73
2012	0.74
2013	0.75
2014	0.76
2015	0.77
2016	0.79