Year	Number of
1990	1.26
1991	1.4
1992	1.53
1993	1.66
1994	1.76
1995	1.81
1996	1.89
1997	2
1998	2.12
1999	2.23
2000	2.33
2001	2.39
2002	2.48
2003	2.64
2004	2.88
2005	3.07
2006	3.22
2007	3.37
2008	3.5
2009	3.62
2010	3.71
2011	3.81
2012	3.91
2013	4
2014	4.1
2015	4.2
2016	4.27