Year	Number of
1990	3.01
1991	3.07
1992	3.16
1993	3.25
1994	3.36
1995	3.46
1996	3.52
1997	3.55
1998	3.63
1999	3.73
2000	3.78
2001	3.87
2002	3.96
2003	4
2004	4.08
2005	4.22
2006	4.33
2007	4.44
2008	4.49
2009	4.49
2010	4.45
2011	4.41
2012	4.37
2013	4.39
2014	4.47
2015	4.6
2016	4.77