Year	Number of
1990	6.08
1991	6.35
1992	6.61
1993	6.88
1994	7.14
1995	7.4
1996	7.61
1997	7.82
1998	8.02
1999	8.17
2000	8.33
2001	8.42
2002	8.6
2003	8.62
2004	8.58
2005	8.77
2006	8.78
2007	8.6
2008	8.43
2009	8.44
2010	8.51
2011	8.22
2012	8.16
2013	8.18
2014	8.45
2015	8.53
2016	8.34