Year	Number of
1990	2.43
1991	2.46
1992	2.51
1993	2.56
1994	2.61
1995	2.66
1996	2.69
1997	2.71
1998	2.75
1999	2.78
2000	2.8
2001	2.84
2002	2.9
2003	2.96
2004	3.02
2005	3.08
2006	3.1
2007	3.16
2008	3.21
2009	3.28
2010	3.36
2011	3.46
2012	3.51
2013	3.56
2014	3.61
2015	3.65
2016	3.65