Year	Years
1970	0.42
1971	0.44
1972	0.45
1973	0.47
1974	0.48
1975	0.5
1976	0.52
1977	0.54
1978	0.56
1979	0.58
1980	0.6
1981	0.62
1982	0.64
1983	0.67
1984	0.69
1985	0.72
1986	0.74
1987	0.77
1988	0.8
1989	0.83
1990	0.86
1991	0.89
1992	0.92
1993	0.96
1994	0.99
1995	1.03
1996	1.07
1997	1.11
1998	1.15
1999	1.2
2000	1.24
2001	1.29
2002	1.34
2003	1.39
2004	1.44
2005	1.49
2006	1.54
2007	1.59
2008	1.65
2009	1.7
2010	1.76
2011	1.82
2012	1.88
2013	1.94
2014	2
2015	2.06