Year	Number of
1990	1.37
1991	1.45
1992	1.51
1993	1.6
1994	1.65
1995	1.55
1996	1.49
1997	1.44
1998	1.4
1999	1.36
2000	1.33
2001	1.3
2002	1.28
2003	1.3
2004	1.41
2005	1.43
2006	1.47
2007	1.5
2008	1.55
2009	1.62
2010	1.64
2011	1.66
2012	1.68
2013	1.7
2014	1.72
2015	1.73
2016	1.73