Year	Number of
1990	3.62
1991	3.79
1992	3.88
1993	3.98
1994	4.06
1995	4.14
1996	4.17
1997	4.17
1998	4.17
1999	4.32
2000	4.37
2001	4.34
2002	4.33
2003	4.32
2004	4.3
2005	4.3
2006	4.27
2007	4.28
2008	4.27
2009	4.28
2010	4.34
2011	4.39
2012	4.44
2013	4.49
2014	4.55
2015	4.62
2016	4.67