Year	Number of
1990	5.08
1991	5.19
1992	5.31
1993	5.43
1994	5.56
1995	5.71
1996	5.72
1997	5.76
1998	5.72
1999	5.59
2000	5.58
2001	5.55
2002	5.6
2003	5.59
2004	5.7
2005	5.81
2006	5.98
2007	6.14
2008	6.33
2009	6.52
2010	6.71
2011	7.03
2012	7.32
2013	7.63
2014	7.97
2015	8.34
2016	8.75