Year	Number of
1990	3.59
1991	3.68
1992	3.77
1993	3.83
1994	3.9
1995	3.95
1996	4
1997	4.06
1998	4.12
1999	4.16
2000	4.18
2001	4.21
2002	4.24
2003	4.27
2004	4.32
2005	4.38
2006	4.43
2007	4.49
2008	4.53
2009	4.62
2010	4.71
2011	4.79
2012	4.9
2013	5
2014	5.13
2015	5.26
2016	5.39