Year	Years
1970	0.61
1971	0.63
1972	0.65
1973	0.67
1974	0.68
1975	0.7
1976	0.72
1977	0.74
1978	0.76
1979	0.79
1980	0.81
1981	0.83
1982	0.85
1983	0.88
1984	0.9
1985	0.93
1986	0.95
1987	0.98
1988	1
1989	1.03
1990	1.06
1991	1.09
1992	1.12
1993	1.15
1994	1.18
1995	1.22
1996	1.25
1997	1.29
1998	1.32
1999	1.36
2000	1.4
2001	1.44
2002	1.47
2003	1.51
2004	1.56
2005	1.6
2006	1.64
2007	1.68
2008	1.73
2009	1.78
2010	1.82
2011	1.87
2012	1.92
2013	1.97
2014	2.02
2015	2.07