Year	Number of
1990	1.35
1991	1.44
1992	1.52
1993	1.6
1994	1.66
1995	1.79
1996	1.89
1997	1.97
1998	2.2
1999	2.17
2000	2.16
2001	2.16
2002	2.24
2003	2.33
2004	2.43
2005	2.55
2006	2.72
2007	2.88
2008	3.01
2009	3.17
2010	3.25
2011	3.42
2012	3.55
2013	3.69
2014	3.85
2015	4
2016	4.14