Year	Number of
1990	4.46
1991	4.63
1992	4.77
1993	4.89
1994	5.02
1995	5.1
1996	5.21
1997	5.23
1998	5.16
1999	5.46
2000	5.48
2001	5.51
2002	5.63
2003	5.7
2004	5.78
2005	5.81
2006	5.84
2007	5.9
2008	6.02
2009	6.05
2010	6.15
2011	6.37
2012	6.53
2013	6.98
2014	7.2
2015	7.32
2016	7.32