Year	Number of
1990	3.11
1991	3.14
1992	3.18
1993	3.23
1994	3.28
1995	3.35
1996	3.36
1997	3.38
1998	3.46
1999	3.5
2000	3.54
2001	3.53
2002	3.55
2003	3.57
2004	3.56
2005	3.57
2006	3.56
2007	3.57
2008	3.59
2009	3.61
2010	3.62
2011	3.64
2012	3.68
2013	3.71
2014	3.75
2015	3.79
2016	3.83