Year	Number of
1990	6.39
1991	6.75
1992	7.12
1993	7.5
1994	7.86
1995	8.26
1996	8.32
1997	8.3
1998	8.32
1999	8.33
2000	8.4
2001	8.51
2002	8.62
2003	8.78
2004	8.96
2005	9.14
2006	9.03
2007	8.99
2008	9.02
2009	9.09
2010	9.19
2011	9.06
2012	8.99
2013	9.04
2014	9.2
2015	9.35
2016	9.54