Year	Number of
1990	2.03
1991	2.11
1992	2.2
1993	2.29
1994	2.38
1995	2.46
1996	2.51
1997	2.53
1998	2.55
1999	2.6
2000	2.63
2001	2.69
2002	2.76
2003	2.81
2004	2.88
2005	2.95
2006	3.03
2007	3.13
2008	3.2
2009	3.24
2010	3.31
2011	3.34
2012	3.35
2013	3.39
2014	3.47
2015	3.65
2016	3.73