Year	Number of
1990	3.26
1991	3.25
1992	3.33
1993	3.37
1994	3.46
1995	3.55
1996	3.47
1997	3.36
1998	3.21
1999	3.04
2000	2.95
2001	2.86
2002	3.03
2003	3.07
2004	3.11
2005	3.16
2006	3.17
2007	3.11
2008	3.09
2009	3.08
2010	3.15
2011	3.27
2012	3.43
2013	3.52
2014	3.73
2015	3.81
2016	3.77