Year	Years
1970	0.63
1971	0.65
1972	0.68
1973	0.71
1974	0.74
1975	0.78
1976	0.81
1977	0.85
1978	0.89
1979	0.93
1980	0.98
1981	1.03
1982	1.08
1983	1.13
1984	1.19
1985	1.25
1986	1.31
1987	1.38
1988	1.45
1989	1.53
1990	1.62
1991	1.71
1992	1.81
1993	1.91
1994	2.02
1995	2.14
1996	2.23
1997	2.32
1998	2.42
1999	2.51
2000	2.61
2001	2.71
2002	2.81
2003	2.91
2004	3.01
2005	3.11
2006	3.21
2007	3.32
2008	3.42
2009	3.53
2010	3.64
2011	3.75
2012	3.86
2013	3.97
2014	4.09
2015	4.21