Year	Years
1970	0.58
1971	0.6
1972	0.62
1973	0.64
1974	0.67
1975	0.69
1976	0.71
1977	0.74
1978	0.76
1979	0.79
1980	0.81
1981	0.84
1982	0.87
1983	0.9
1984	0.93
1985	0.96
1986	0.99
1987	1.03
1988	1.06
1989	1.1
1990	1.13
1991	1.17
1992	1.21
1993	1.25
1994	1.29
1995	1.34
1996	1.38
1997	1.43
1998	1.47
1999	1.52
2000	1.57
2001	1.62
2002	1.67
2003	1.73
2004	1.78
2005	1.84
2006	1.89
2007	1.95
2008	2.02
2009	2.08
2010	2.14
2011	2.21
2012	2.28
2013	2.35
2014	2.42
2015	2.49