Year	Number of
1990	1.06
1991	1.08
1992	1.11
1993	1.14
1994	1.18
1995	1.23
1996	1.26
1997	1.31
1998	1.39
1999	1.37
2000	1.34
2001	1.38
2002	1.34
2003	1.36
2004	1.38
2005	1.48
2006	1.57
2007	1.68
2008	1.83
2009	1.9
2010	2.01
2011	2.11
2012	2.23
2013	2.34
2014	2.46
2015	2.58
2016	2.67