Year	Years
1970	0.61
1971	0.63
1972	0.65
1973	0.67
1974	0.69
1975	0.71
1976	0.73
1977	0.76
1978	0.78
1979	0.81
1980	0.83
1981	0.86
1982	0.88
1983	0.91
1984	0.94
1985	0.97
1986	1
1987	1.03
1988	1.06
1989	1.09
1990	1.13
1991	1.16
1992	1.2
1993	1.23
1994	1.27
1995	1.31
1996	1.35
1997	1.39
1998	1.44
1999	1.48
2000	1.53
2001	1.58
2002	1.63
2003	1.68
2004	1.73
2005	1.78
2006	1.84
2007	1.9
2008	1.96
2009	2.02
2010	2.08
2011	2.15
2012	2.21
2013	2.28
2014	2.35
2015	2.42