Year	Number of
1990	8.44
1991	8.41
1992	8.46
1993	8.49
1994	8.95
1995	8.99
1996	8.73
1997	9.1
1998	9.59
1999	9.84
2000	10.49
2001	10.96
2002	11.59
2003	11.7
2004	11.64
2005	11.8
2006	11.67
2007	11.39
2008	11.97
2009	12.36
2010	13.13
2011	13.77
2012	14.65
2013	15.31
2014	16.24
2015	17.04
2016	18.13