Year	Number of
1990	8.62
1991	8.72
1992	9.08
1993	9.33
1994	9.44
1995	9.43
1996	9.44
1997	9.55
1998	9.84
1999	10.09
2000	10.46
2001	10.66
2002	11.09
2003	11.35
2004	11.58
2005	11.79
2006	12.01
2007	12.14
2008	12.36
2009	12.62
2010	12.99
2011	13.42
2012	13.91
2013	14.43
2014	15.07
2015	15.49
2016	15.89