Year	Number of
1990	1.51
1991	1.58
1992	1.66
1993	1.74
1994	1.82
1995	1.89
1996	1.95
1997	2
1998	2.06
1999	2.12
2000	2.18
2001	2.27
2002	2.36
2003	2.45
2004	2.54
2005	2.65
2006	2.71
2007	2.78
2008	2.83
2009	2.88
2010	2.93
2011	2.95
2012	2.98
2013	3.03
2014	3.09
2015	3.16
2016	3.25