Year	Number of
1990	5.99
1991	6.01
1992	6.04
1993	6.21
1994	6.33
1995	6.27
1996	6.69
1997	6.33
1998	6.42
1999	6.81
2000	7.14
2001	6.84
2002	7.03
2003	7.15
2004	7.06
2005	6.99
2006	7.22
2007	7.31
2008	7.65
2009	7.78
2010	8.06
2011	8.12
2012	8.35
2013	8.47
2014	8.47
2015	8.22
2016	8.69