Year	Number of
1990	8.15
1991	8.46
1992	8.7
1993	8.91
1994	9.14
1995	9.4
1996	9.73
1997	10.08
1998	10.43
1999	10.68
2000	10.94
2001	11.2
2002	11.54
2003	11.99
2004	12.45
2005	12.97
2006	13.51
2007	14.14
2008	14.8
2009	15.43
2010	16.09
2011	16.79
2012	17.55
2013	18.28
2014	18.91
2015	19.69
2016	20.45