Year	Number of
1990	6.13
1991	6.13
1992	6.08
1993	6.03
1994	6.04
1995	6.22
1996	6.66
1997	6.86
1998	6.83
1999	6.81
2000	6.75
2001	6.88
2002	6.86
2003	6.91
2004	6.99
2005	7.06
2006	6.9
2007	6.83
2008	7
2009	7.18
2010	6.98
2011	6.56
2012	6.16
2013	6.08
2014	6.16
2015	6.39
2016	6.69