Year	Years
1970	0.41
1971	0.43
1972	0.44
1973	0.45
1974	0.46
1975	0.48
1976	0.49
1977	0.51
1978	0.52
1979	0.54
1980	0.55
1981	0.57
1982	0.59
1983	0.6
1984	0.62
1985	0.64
1986	0.66
1987	0.68
1988	0.7
1989	0.72
1990	0.74
1991	0.77
1992	0.79
1993	0.82
1994	0.84
1995	0.87
1996	0.9
1997	0.93
1998	0.96
1999	0.99
2000	1.02
2001	1.05
2002	1.09
2003	1.12
2004	1.15
2005	1.19
2006	1.22
2007	1.26
2008	1.3
2009	1.33
2010	1.37
2011	1.41
2012	1.45
2013	1.49
2014	1.53
2015	1.58