Year	Number of
1990	1.9
1991	1.96
1992	2.02
1993	2.09
1994	2.16
1995	2.23
1996	2.31
1997	2.38
1998	2.44
1999	2.51
2000	2.6
2001	2.64
2002	2.69
2003	2.74
2004	2.81
2005	2.87
2006	2.91
2007	2.95
2008	2.99
2009	3.05
2010	3.11
2011	3.15
2012	3.22
2013	3.25
2014	3.29
2015	3.35
2016	3.4