Year	Number of
1990	0.64
1991	0.65
1992	0.66
1993	0.66
1994	0.67
1995	0.68
1996	0.75
1997	0.81
1998	0.9
1999	0.94
2000	1.02
2001	1.08
2002	1.09
2003	1.12
2004	1.15
2005	1.14
2006	1.1
2007	1.1
2008	1.15
2009	1.18
2010	1.16
2011	1.12
2012	1.06
2013	1.06
2014	1.06
2015	1.09
2016	1.13