Year	Number of
1990	1.66
1991	1.74
1992	1.82
1993	1.92
1994	2.01
1995	2.1
1996	2.17
1997	2.22
1998	2.27
1999	2.33
2000	2.39
2001	2.47
2002	2.55
2003	2.63
2004	2.73
2005	2.83
2006	2.93
2007	3.03
2008	3.12
2009	3.2
2010	3.28
2011	3.34
2012	3.4
2013	3.49
2014	3.59
2015	3.7
2016	3.82