Year	Number of
1990	0.65
1991	0.66
1992	0.68
1993	0.7
1994	0.73
1995	0.76
1996	0.77
1997	0.78
1998	0.82
1999	0.77
2000	0.72
2001	0.68
2002	0.71
2003	0.73
2004	0.75
2005	0.78
2006	0.81
2007	0.84
2008	0.86
2009	0.88
2010	0.88
2011	0.93
2012	0.96
2013	1
2014	1.04
2015	1.08
2016	1.09