Year	Number of
1990	0.94
1991	0.97
1992	0.99
1993	1.01
1994	1.04
1995	1.07
1996	1.11
1997	1.14
1998	1.19
1999	1.22
2000	1.27
2001	1.31
2002	1.34
2003	1.38
2004	1.4
2005	1.45
2006	1.49
2007	1.51
2008	1.56
2009	1.63
2010	1.72
2011	1.74
2012	1.8
2013	1.88
2014	1.93
2015	1.98
2016	2.04