Year	Number of
1990	7.6
1991	7.64
1992	7.67
1993	7.6
1994	7.59
1995	7.57
1996	7.58
1997	7.42
1998	7.43
1999	7.1
2000	6.82
2001	6.64
2002	6.66
2003	6.57
2004	6.4
2005	6.44
2006	6.45
2007	6.47
2008	6.61
2009	6.7
2010	6.94
2011	7.15
2012	7.32
2013	7.63
2014	7.9
2015	8.14
2016	8.73