Year	Number of
1990	1.34
1991	1.37
1992	1.41
1993	1.45
1994	1.49
1995	1.54
1996	1.58
1997	1.62
1998	1.67
1999	1.72
2000	1.78
2001	1.83
2002	1.87
2003	1.93
2004	1.99
2005	2.05
2006	2.12
2007	2.2
2008	2.28
2009	2.36
2010	2.45
2011	2.55
2012	2.68
2013	2.82
2014	2.95
2015	3.1
2016	3.25