Year	Number of
1990	1.19
1991	1.24
1992	1.29
1993	1.35
1994	1.4
1995	1.46
1996	1.52
1997	1.58
1998	1.68
1999	1.76
2000	1.87
2001	1.89
2002	1.94
2003	2.01
2004	2.1
2005	2.18
2006	2.29
2007	2.36
2008	2.41
2009	2.49
2010	2.57
2011	2.7
2012	2.81
2013	2.91
2014	3.02
2015	3.13
2016	3.24