Year	Years
1970	0.41
1971	0.42
1972	0.44
1973	0.46
1974	0.47
1975	0.49
1976	0.51
1977	0.53
1978	0.56
1979	0.58
1980	0.6
1981	0.63
1982	0.66
1983	0.68
1984	0.71
1985	0.74
1986	0.78
1987	0.81
1988	0.85
1989	0.88
1990	0.92
1991	0.97
1992	1.01
1993	1.06
1994	1.11
1995	1.16
1996	1.21
1997	1.27
1998	1.32
1999	1.38
2000	1.43
2001	1.49
2002	1.55
2003	1.61
2004	1.67
2005	1.74
2006	1.8
2007	1.87
2008	1.93
2009	2
2010	2.07
2011	2.13
2012	2.2
2013	2.27
2014	2.34
2015	2.41