Year	Number of
1990	6.26
1991	6.41
1992	6.57
1993	6.74
1994	6.93
1995	7.16
1996	7.19
1997	7.28
1998	7.22
1999	6.98
2000	6.95
2001	6.88
2002	7
2003	6.99
2004	7.14
2005	7.31
2006	7.58
2007	7.83
2008	8.11
2009	8.33
2010	8.58
2011	9.03
2012	9.41
2013	9.8
2014	10.22
2015	10.7
2016	11.2