Year	Years
1970	0.52
1971	0.54
1972	0.56
1973	0.57
1974	0.59
1975	0.61
1976	0.62
1977	0.64
1978	0.66
1979	0.68
1980	0.7
1981	0.72
1982	0.74
1983	0.76
1984	0.79
1985	0.81
1986	0.83
1987	0.86
1988	0.88
1989	0.91
1990	0.94
1991	0.96
1992	0.99
1993	1.02
1994	1.05
1995	1.08
1996	1.11
1997	1.14
1998	1.17
1999	1.21
2000	1.24
2001	1.27
2002	1.31
2003	1.34
2004	1.38
2005	1.42
2006	1.45
2007	1.49
2008	1.53
2009	1.57
2010	1.61
2011	1.65
2012	1.69
2013	1.73
2014	1.78
2015	1.82