Year	Number of
1990	0.93
1991	0.95
1992	0.97
1993	0.98
1994	1.01
1995	1.03
1996	1.05
1997	1.06
1998	1.08
1999	1.1
2000	1.11
2001	1.14
2002	1.16
2003	1.19
2004	1.23
2005	1.26
2006	1.28
2007	1.29
2008	1.31
2009	1.33
2010	1.36
2011	1.38
2012	1.41
2013	1.43
2014	1.46
2015	1.49
2016	1.52