Year	Number of
1990	7.79
1991	7.86
1992	7.92
1993	7.92
1994	7.89
1995	7.99
1996	8.1
1997	8.13
1998	8.28
1999	8.57
2000	8.73
2001	8.96
2002	9.11
2003	9.66
2004	9.97
2005	10.28
2006	10.33
2007	10.39
2008	10.54
2009	10.5
2010	10.73
2011	10.86
2012	11.24
2013	11.71
2014	12.4
2015	12.75
2016	13.15