Year	Number of
1990	3.35
1991	3.55
1992	3.7
1993	3.88
1994	3.97
1995	3.8
1996	3.69
1997	3.62
1998	3.55
1999	3.51
2000	3.44
2001	3.38
2002	3.35
2003	3.43
2004	3.67
2005	3.74
2006	3.8
2007	3.86
2008	3.95
2009	4.05
2010	4.06
2011	4.06
2012	4.06
2013	4.07
2014	4.07
2015	4.08
2016	4.08