Year	Number of
1990	1.22
1991	1.28
1992	1.37
1993	1.45
1994	1.53
1995	1.62
1996	1.71
1997	1.8
1998	1.86
1999	1.92
2000	2
2001	2.09
2002	2.19
2003	2.26
2004	2.34
2005	2.4
2006	2.51
2007	2.61
2008	2.69
2009	2.8
2010	2.89
2011	3.11
2012	3.26
2013	3.39
2014	3.52
2015	3.64
2016	3.75