Year	Number of
1990	5.29
1991	5.7
1992	6.13
1993	6.54
1994	6.94
1995	7.33
1996	7.64
1997	7.98
1998	8.26
1999	8.4
2000	8.61
2001	8.79
2002	8.9
2003	8.96
2004	9.13
2005	9.45
2006	9.95
2007	10.65
2008	11.42
2009	12.21
2010	12.97
2011	13.55
2012	14.06
2013	14.5
2014	14.96
2015	15.53
2016	16.49