Year	Number of
1990	0.78
1991	0.85
1992	0.91
1993	0.97
1994	1.03
1995	1.01
1996	1.02
1997	1.04
1998	1.06
1999	1.07
2000	1.08
2001	1.08
2002	1.09
2003	1.13
2004	1.23
2005	1.27
2006	1.31
2007	1.36
2008	1.4
2009	1.45
2010	1.47
2011	1.51
2012	1.54
2013	1.56
2014	1.59
2015	1.62
2016	1.62