Year	Number of
1990	7.96
1991	8.19
1992	8.41
1993	8.64
1994	8.88
1995	9.16
1996	9.37
1997	9.62
1998	9.78
1999	9.79
2000	9.97
2001	10.09
2002	10.4
2003	10.62
2004	10.92
2005	11.3
2006	11.74
2007	12.17
2008	12.62
2009	12.99
2010	13.45
2011	13.97
2012	14.42
2013	14.85
2014	15.32
2015	15.8
2016	16.35