Year	Number of
1990	2.99
1991	3.11
1992	3.22
1993	3.33
1994	3.43
1995	3.52
1996	3.6
1997	3.68
1998	3.76
1999	3.86
2000	3.97
2001	4.08
2002	4.21
2003	4.35
2004	4.51
2005	4.67
2006	4.85
2007	5.04
2008	5.25
2009	5.48
2010	5.73
2011	5.92
2012	6.14
2013	6.4
2014	6.67
2015	6.95
2016	7.22