Year	Number of
1990	1.38
1991	1.42
1992	1.48
1993	1.51
1994	1.54
1995	1.56
1996	1.59
1997	1.63
1998	1.68
1999	1.73
2000	1.78
2001	1.84
2002	1.91
2003	1.99
2004	2.08
2005	2.15
2006	2.25
2007	2.34
2008	2.42
2009	2.5
2010	2.59
2011	2.69
2012	2.8
2013	2.92
2014	3.04
2015	3.16
2016	3.28