Year	Years
1970	0.51
1971	0.53
1972	0.55
1973	0.56
1974	0.58
1975	0.6
1976	0.62
1977	0.64
1978	0.67
1979	0.69
1980	0.71
1981	0.74
1982	0.76
1983	0.79
1984	0.81
1985	0.84
1986	0.87
1987	0.9
1988	0.93
1989	0.96
1990	0.99
1991	1.02
1992	1.06
1993	1.09
1994	1.13
1995	1.17
1996	1.21
1997	1.25
1998	1.29
1999	1.33
2000	1.38
2001	1.42
2002	1.47
2003	1.52
2004	1.57
2005	1.62
2006	1.67
2007	1.72
2008	1.78
2009	1.83
2010	1.89
2011	1.95
2012	2.01
2013	2.07
2014	2.14
2015	2.2