Year	Years
1970	0.43
1971	0.44
1972	0.46
1973	0.47
1974	0.49
1975	0.51
1976	0.52
1977	0.54
1978	0.56
1979	0.58
1980	0.6
1981	0.62
1982	0.64
1983	0.66
1984	0.68
1985	0.71
1986	0.73
1987	0.75
1988	0.78
1989	0.8
1990	0.83
1991	0.86
1992	0.89
1993	0.92
1994	0.95
1995	0.98
1996	1.01
1997	1.04
1998	1.08
1999	1.11
2000	1.15
2001	1.18
2002	1.22
2003	1.26
2004	1.3
2005	1.34
2006	1.39
2007	1.43
2008	1.48
2009	1.52
2010	1.57
2011	1.62
2012	1.67
2013	1.73
2014	1.78
2015	1.83