Year	Number of
1990	1.23
1991	1.3
1992	1.38
1993	1.46
1994	1.55
1995	1.65
1996	1.75
1997	1.85
1998	1.97
1999	2.08
2000	2.2
2001	2.37
2002	2.55
2003	2.73
2004	2.92
2005	3.13
2006	3.25
2007	3.38
2008	3.53
2009	3.69
2010	3.85
2011	4
2012	4.16
2013	4.34
2014	4.53
2015	4.71
2016	4.9