Year	Number of
1990	0.88
1991	0.91
1992	0.94
1993	0.96
1994	0.99
1995	1.01
1996	1.04
1997	1.07
1998	1.1
1999	1.14
2000	1.18
2001	1.22
2002	1.27
2003	1.33
2004	1.39
2005	1.45
2006	1.5
2007	1.54
2008	1.59
2009	1.64
2010	1.7
2011	1.75
2012	1.8
2013	1.86
2014	1.92
2015	1.98
2016	2.1