Year	Number of
1990	1.93
1991	2.02
1992	2.11
1993	2.21
1994	2.33
1995	2.45
1996	2.57
1997	2.69
1998	2.82
1999	2.98
2000	3.15
2001	3.32
2002	3.48
2003	3.64
2004	3.79
2005	3.95
2006	4.12
2007	4.27
2008	4.5
2009	4.75
2010	4.99
2011	5.15
2012	5.32
2013	5.48
2014	5.65
2015	5.84
2016	6.09