Year	Number of
1990	3.13
1991	3.28
1992	3.47
1993	3.74
1994	4.13
1995	4.73
1996	5.48
1997	6.2
1998	6.66
1999	7.05
2000	7.49
2001	7.9
2002	8.39
2003	8.99
2004	9.62
2005	10.24
2006	10.73
2007	11.18
2008	11.7
2009	12.21
2010	12.7
2011	12.74
2012	13.26
2013	13.21
2014	13.26
2015	13.35
2016	13.46