Year	Number of
1990	4.68
1991	4.71
1992	4.77
1993	4.9
1994	5.02
1995	5.18
1996	5.33
1997	5.4
1998	5.51
1999	5.62
2000	5.82
2001	6
2002	6.33
2003	6.58
2004	6.72
2005	6.79
2006	6.94
2007	7.1
2008	7.15
2009	7.22
2010	7.39
2011	7.62
2012	7.85
2013	8.19
2014	8.47
2015	8.49
2016	8.31