Year	Number of
1990	9.19
1991	9.3
1992	9.55
1993	9.51
1994	9.7
1995	9.9
1996	9.51
1997	9.14
1998	8.7
1999	8.3
2000	8.23
2001	7.59
2002	7.77
2003	7.77
2004	7.88
2005	7.84
2006	7.81
2007	7.7
2008	7.65
2009	7.68
2010	7.78
2011	8.04
2012	8.25
2013	8.51
2014	8.84
2015	9.2
2016	9.52