Year	Years
1970	0.43
1971	0.44
1972	0.46
1973	0.48
1974	0.49
1975	0.51
1976	0.53
1977	0.55
1978	0.57
1979	0.59
1980	0.61
1981	0.63
1982	0.66
1983	0.68
1984	0.71
1985	0.73
1986	0.76
1987	0.79
1988	0.82
1989	0.85
1990	0.88
1991	0.91
1992	0.95
1993	0.98
1994	1.02
1995	1.06
1996	1.11
1997	1.15
1998	1.2
1999	1.24
2000	1.29
2001	1.34
2002	1.39
2003	1.44
2004	1.5
2005	1.55
2006	1.61
2007	1.66
2008	1.72
2009	1.78
2010	1.84
2011	1.9
2012	1.97
2013	2.03
2014	2.09
2015	2.16