Year	Number of
1990	4.51
1991	4.45
1992	4.47
1993	4.36
1994	4.46
1995	4.34
1996	4.27
1997	4.22
1998	4.13
1999	4.01
2000	3.99
2001	4.02
2002	4.11
2003	4.07
2004	4.03
2005	3.87
2006	3.76
2007	3.52
2008	3.5
2009	3.46
2010	3.47
2011	3.47
2012	3.53
2013	3.53
2014	3.61
2015	3.61
2016	3.62