Year	Number of
1990	5.56
1991	5.53
1992	5.51
1993	5.41
1994	5.36
1995	5.31
1996	5.28
1997	5.2
1998	5.15
1999	5.13
2000	5.11
2001	5.03
2002	4.9
2003	4.7
2004	4.5
2005	4.37
2006	4.24
2007	4.08
2008	3.96
2009	3.93
2010	3.9
2011	4.18
2012	4.15
2013	4.24
2014	4.33
2015	4.45
2016	4.61