Year	Number of
1990	3.18
1991	3.25
1992	3.32
1993	3.4
1994	3.48
1995	3.57
1996	3.61
1997	3.67
1998	3.74
1999	3.81
2000	3.88
2001	3.94
2002	4.01
2003	4.08
2004	4.15
2005	4.22
2006	4.25
2007	4.28
2008	4.31
2009	4.33
2010	4.36
2011	4.41
2012	4.45
2013	4.49
2014	4.53
2015	4.59
2016	4.66