Year	Number of
1990	0.74
1991	0.76
1992	0.77
1993	0.78
1994	0.8
1995	0.81
1996	0.83
1997	0.85
1998	0.88
1999	0.9
2000	0.93
2001	0.96
2002	0.98
2003	1.02
2004	1.05
2005	1.08
2006	1.12
2007	1.14
2008	1.16
2009	1.19
2010	1.22
2011	1.25
2012	1.29
2013	1.34
2014	1.39
2015	1.43
2016	1.48