Year	Number of
1990	7.35
1991	7.77
1992	8.2
1993	8.37
1994	8.37
1995	8.31
1996	8.39
1997	8.54
1998	8.7
1999	9.1
2000	9.17
2001	9.16
2002	9.3
2003	9.08
2004	9.02
2005	8.83
2006	8.66
2007	8.56
2008	8.56
2009	8.58
2010	8.43
2011	8.22
2012	7.91
2013	7.89
2014	7.92
2015	7.74
2016	7.87