Year	Number of
1990	3.67
1991	4.06
1992	4.52
1993	5.06
1994	5.69
1995	6.4
1996	6.85
1997	7.33
1998	7.85
1999	8.41
2000	9.04
2001	9.22
2002	9.45
2003	9.68
2004	9.94
2005	10.22
2006	10.59
2007	10.99
2008	11.48
2009	12.03
2010	12.63
2011	13.18
2012	13.76
2013	14.34
2014	14.97
2015	15.64
2016	16.39