Year	Years
1970	1.87
1971	1.88
1972	1.88
1973	1.88
1974	1.88
1975	1.87
1976	1.86
1977	1.85
1978	1.84
1979	1.83
1980	1.82
1981	1.8
1982	1.79
1983	1.78
1984	1.76
1985	1.75
1986	1.74
1987	1.73
1988	1.72
1989	1.71
1990	1.7
1991	1.7
1992	1.7
1993	1.69
1994	1.7
1995	1.7
1996	1.72
1997	1.75
1998	1.77
1999	1.8
2000	1.84
2001	1.87
2002	1.91
2003	1.95
2004	1.99
2005	2.03
2006	2.08
2007	2.13
2008	2.18
2009	2.24
2010	2.3
2011	2.35
2012	2.41
2013	2.48
2014	2.54
2015	2.61