Year	Number of
1990	8.69
1991	8.79
1992	8.9
1993	9.02
1994	9.16
1995	9.33
1996	8.93
1997	8.57
1998	8.2
1999	7.85
2000	7.51
2001	7.41
2002	7.31
2003	7.21
2004	7.11
2005	7.01
2006	7
2007	7
2008	7.01
2009	7.02
2010	7.04
2011	7.26
2012	7.49
2013	7.72
2014	7.97
2015	8.22
2016	8.49