Year	Number of
1990	0.96
1991	0.98
1992	1
1993	1.01
1994	1.03
1995	1.04
1996	1.05
1997	1.06
1998	1.06
1999	1.07
2000	1.07
2001	1.11
2002	1.15
2003	1.19
2004	1.23
2005	1.28
2006	1.33
2007	1.37
2008	1.41
2009	1.44
2010	1.48
2011	1.54
2012	1.61
2013	1.69
2014	1.78
2015	1.86
2016	1.96