Year	Number of
1990	0.53
1991	0.56
1992	0.58
1993	0.6
1994	0.63
1995	0.65
1996	0.66
1997	0.68
1998	0.7
1999	0.71
2000	0.74
2001	0.76
2002	0.8
2003	0.83
2004	0.88
2005	0.92
2006	0.95
2007	0.98
2008	1.01
2009	1.04
2010	1.07
2011	1.09
2012	1.12
2013	1.15
2014	1.18
2015	1.22
2016	1.28