Year	Number of
1990	0.58
1991	0.6
1992	0.63
1993	0.66
1994	0.68
1995	0.7
1996	0.73
1997	0.75
1998	0.76
1999	0.78
2000	0.79
2001	0.82
2002	0.86
2003	0.88
2004	0.9
2005	0.91
2006	0.94
2007	0.97
2008	0.99
2009	1.02
2010	1.04
2011	1.12
2012	1.16
2013	1.2
2014	1.23
2015	1.26
2016	1.28