Year	Number of
1990	4.68
1991	4.65
1992	4.6
1993	4.54
1994	4.52
1995	4.49
1996	4.45
1997	4.26
1998	4.31
1999	4.4
2000	4.47
2001	4.32
2002	4.29
2003	4.12
2004	4.03
2005	3.86
2006	3.68
2007	3.42
2008	3.42
2009	3.36
2010	3.33
2011	3.35
2012	3.4
2013	3.46
2014	3.56
2015	3.55
2016	3.6