Year	Number of
1990	1.15
1991	1.18
1992	1.21
1993	1.23
1994	1.22
1995	1.24
1996	1.25
1997	1.28
1998	1.3
1999	1.32
2000	1.34
2001	1.38
2002	1.42
2003	1.47
2004	1.52
2005	1.57
2006	1.64
2007	1.68
2008	1.71
2009	1.75
2010	1.78
2011	1.81
2012	1.84
2013	1.87
2014	1.9
2015	1.93
2016	2