Year	Number of
1990	1.21
1991	1.31
1992	1.42
1993	1.54
1994	1.67
1995	1.81
1996	1.94
1997	2.08
1998	2.23
1999	2.39
2000	2.56
2001	2.77
2002	3
2003	3.24
2004	3.51
2005	3.8
2006	3.97
2007	4.16
2008	4.35
2009	4.55
2010	4.76
2011	4.95
2012	5.15
2013	5.36
2014	5.58
2015	5.8
2016	6.04