Year	Number of
1990	0.78
1991	0.81
1992	0.84
1993	0.85
1994	0.86
1995	0.87
1996	0.88
1997	0.9
1998	0.92
1999	0.95
2000	0.98
2001	1.02
2002	1.06
2003	1.11
2004	1.17
2005	1.22
2006	1.28
2007	1.32
2008	1.37
2009	1.41
2010	1.46
2011	1.51
2012	1.55
2013	1.6
2014	1.65
2015	1.7
2016	1.79