Year	Number of
1990	6.45
1991	6.53
1992	6.64
1993	6.83
1994	7.04
1995	7.22
1996	7.79
1997	8.43
1998	9.06
1999	9.8
2000	10.62
2001	11.09
2002	11.51
2003	12.01
2004	12.41
2005	13.01
2006	13.95
2007	14.55
2008	15.19
2009	16.09
2010	16.57
2011	16.82
2012	17.34
2013	18
2014	19.16
2015	20.06
2016	21.14