Year	Number of
1990	3.88
1991	3.9
1992	3.92
1993	3.95
1994	3.98
1995	4.02
1996	4.15
1997	4.31
1998	4.49
1999	4.67
2000	4.85
2001	5
2002	5.16
2003	5.4
2004	5.64
2005	5.9
2006	6.01
2007	6.09
2008	6.12
2009	6.15
2010	6.23
2011	6.42
2012	6.67
2013	6.85
2014	7.02
2015	7.15
2016	7.34