Year	Number of
1990	4.24
1991	4.23
1992	4.19
1993	4.15
1994	4.14
1995	4.14
1996	4.09
1997	3.93
1998	3.98
1999	4.03
2000	4.09
2001	3.94
2002	3.9
2003	3.75
2004	3.68
2005	3.54
2006	3.41
2007	3.21
2008	3.21
2009	3.19
2010	3.18
2011	3.2
2012	3.24
2013	3.31
2014	3.4
2015	3.4
2016	3.46