Year	Years
1970	0.53
1971	0.54
1972	0.56
1973	0.57
1974	0.59
1975	0.61
1976	0.62
1977	0.64
1978	0.66
1979	0.68
1980	0.7
1981	0.72
1982	0.74
1983	0.76
1984	0.78
1985	0.8
1986	0.82
1987	0.85
1988	0.87
1989	0.9
1990	0.92
1991	0.95
1992	0.97
1993	1
1994	1.03
1995	1.06
1996	1.09
1997	1.12
1998	1.15
1999	1.18
2000	1.21
2001	1.24
2002	1.28
2003	1.31
2004	1.35
2005	1.38
2006	1.42
2007	1.46
2008	1.49
2009	1.53
2010	1.57
2011	1.61
2012	1.65
2013	1.7
2014	1.74
2015	1.79