Year	Number of
1990	6.69
1991	6.94
1992	7.11
1993	7.14
1994	7.12
1995	7.08
1996	7
1997	6.73
1998	6.51
1999	6.48
2000	6.44
2001	6.43
2002	6.48
2003	6.6
2004	6.91
2005	7.1
2006	7.34
2007	7.56
2008	7.68
2009	7.88
2010	8.01
2011	8.36
2012	8.82
2013	9.27
2014	9.63
2015	9.98
2016	10.36