Year	Number of
1990	0.74
1991	0.76
1992	0.79
1993	0.82
1994	0.84
1995	0.87
1996	0.89
1997	0.91
1998	0.97
1999	0.99
2000	1.06
2001	1.08
2002	1.22
2003	1.33
2004	1.43
2005	1.47
2006	1.52
2007	1.57
2008	1.58
2009	1.63
2010	1.64
2011	1.76
2012	1.85
2013	1.89
2014	1.94
2015	1.99
2016	2.04