Year	Number of
1990	8.62
1991	8.78
1992	8.93
1993	9.08
1994	9.24
1995	9.38
1996	9.64
1997	9.88
1998	9.92
1999	10.46
2000	10.75
2001	11.02
2002	11.32
2003	11.73
2004	12.46
2005	13.22
2006	13.94
2007	14.34
2008	14.45
2009	15.02
2010	15.54
2011	16.31
2012	16.85
2013	17.55
2014	18.27
2015	19.01
2016	19.75