Year	Years
1970	0.51
1971	0.52
1972	0.54
1973	0.56
1974	0.57
1975	0.59
1976	0.61
1977	0.63
1978	0.65
1979	0.68
1980	0.7
1981	0.72
1982	0.75
1983	0.77
1984	0.8
1985	0.83
1986	0.86
1987	0.89
1988	0.92
1989	0.96
1990	0.99
1991	1.03
1992	1.07
1993	1.11
1994	1.16
1995	1.21
1996	1.27
1997	1.33
1998	1.39
1999	1.46
2000	1.52
2001	1.58
2002	1.65
2003	1.71
2004	1.78
2005	1.85
2006	1.91
2007	1.98
2008	2.05
2009	2.12
2010	2.19
2011	2.26
2012	2.34
2013	2.41
2014	2.48
2015	2.56