Year	Years
1970	0.33
1971	0.34
1972	0.36
1973	0.37
1974	0.38
1975	0.4
1976	0.41
1977	0.42
1978	0.44
1979	0.46
1980	0.47
1981	0.49
1982	0.51
1983	0.53
1984	0.54
1985	0.56
1986	0.59
1987	0.61
1988	0.63
1989	0.65
1990	0.68
1991	0.7
1992	0.73
1993	0.76
1994	0.78
1995	0.81
1996	0.84
1997	0.87
1998	0.9
1999	0.93
2000	0.96
2001	0.99
2002	1.03
2003	1.06
2004	1.09
2005	1.13
2006	1.17
2007	1.21
2008	1.25
2009	1.29
2010	1.33
2011	1.37
2012	1.42
2013	1.46
2014	1.51
2015	1.56