Year	Number of
1990	3.01
1991	3.37
1992	3.68
1993	4.01
1994	4.32
1995	4.68
1996	4.89
1997	5.08
1998	5.23
1999	5.38
2000	5.43
2001	5.67
2002	5.85
2003	5.9
2004	5.78
2005	5.75
2006	5.7
2007	5.62
2008	5.85
2009	6.19
2010	6.6
2011	6.95
2012	7.32
2013	7.73
2014	8.11
2015	8.32
2016	8.75