Year	Number of
1990	3.54
1991	3.79
1992	4.05
1993	4.36
1994	4.68
1995	5.06
1996	5.19
1997	5.31
1998	5.33
1999	6.17
2000	6.32
2001	6.64
2002	6.85
2003	6.64
2004	6.6
2005	6.62
2006	6.83
2007	7.02
2008	7.04
2009	7.58
2010	8.02
2011	8.13
2012	8.31
2013	8.64
2014	8.98
2015	9.34
2016	9.65