Year	Number of
1990	1.18
1991	1.22
1992	1.25
1993	1.3
1994	1.33
1995	1.37
1996	1.41
1997	1.44
1998	1.47
1999	1.52
2000	1.55
2001	1.61
2002	1.67
2003	1.74
2004	1.82
2005	1.9
2006	1.98
2007	2.01
2008	2.05
2009	2.08
2010	2.11
2011	2.13
2012	2.15
2013	2.17
2014	2.19
2015	2.21
2016	2.26