Year	Number of
1990	5.53
1991	5.55
1992	5.6
1993	5.67
1994	5.64
1995	5.74
1996	5.94
1997	6.1
1998	6.32
1999	6.4
2000	6.49
2001	6.65
2002	6.78
2003	6.93
2004	7.08
2005	7.23
2006	7.27
2007	7.2
2008	7.21
2009	7.28
2010	7.25
2011	7.34
2012	7.64
2013	7.68
2014	7.82
2015	8.04
2016	8.31