Year	Number of
1990	0.82
1991	0.84
1992	0.86
1993	0.87
1994	0.88
1995	0.88
1996	0.9
1997	0.92
1998	0.93
1999	0.95
2000	0.98
2001	1.01
2002	1.05
2003	1.09
2004	1.13
2005	1.17
2006	1.22
2007	1.27
2008	1.31
2009	1.36
2010	1.4
2011	1.45
2012	1.5
2013	1.54
2014	1.59
2015	1.64
2016	1.72