Year	Number of
1990	1.37
1991	1.42
1992	1.48
1993	1.54
1994	1.59
1995	1.66
1996	1.7
1997	1.75
1998	1.79
1999	1.84
2000	1.89
2001	1.95
2002	2.03
2003	2.12
2004	2.21
2005	2.31
2006	2.41
2007	2.5
2008	2.61
2009	2.73
2010	2.87
2011	2.98
2012	3.11
2013	3.25
2014	3.4
2015	3.54
2016	3.7