Year	Number of
1990	5.53
1991	5.63
1992	5.75
1993	5.87
1994	5.98
1995	6.1
1996	6.18
1997	6.25
1998	6.29
1999	6.32
2000	6.35
2001	6.4
2002	6.51
2003	6.64
2004	6.78
2005	6.92
2006	7.09
2007	7.26
2008	7.43
2009	7.64
2010	7.86
2011	7.99
2012	8.2
2013	8.43
2014	8.66
2015	8.9
2016	9.14