Year	Number of
1990	0.68
1991	0.71
1992	0.75
1993	0.79
1994	0.83
1995	0.88
1996	0.94
1997	1
1998	1.06
1999	1.13
2000	1.21
2001	1.31
2002	1.42
2003	1.54
2004	1.67
2005	1.81
2006	1.91
2007	2.02
2008	2.13
2009	2.26
2010	2.39
2011	2.47
2012	2.55
2013	2.64
2014	2.73
2015	2.82
2016	2.92