Year	Number of
1990	3.62
1991	3.68
1992	3.71
1993	3.7
1994	3.66
1995	3.61
1996	3.53
1997	3.43
1998	3.38
1999	3.33
2000	3.31
2001	3.28
2002	3.25
2003	3.2
2004	3.13
2005	3.1
2006	3.09
2007	3.09
2008	3.12
2009	3.18
2010	3.24
2011	3.24
2012	3.24
2013	3.27
2014	3.39
2015	3.5
2016	3.62