Year	Years
1970	0.44
1971	0.46
1972	0.47
1973	0.49
1974	0.51
1975	0.52
1976	0.54
1977	0.56
1978	0.58
1979	0.6
1980	0.62
1981	0.65
1982	0.67
1983	0.69
1984	0.72
1985	0.74
1986	0.77
1987	0.79
1988	0.82
1989	0.85
1990	0.88
1991	0.91
1992	0.94
1993	0.97
1994	1.01
1995	1.04
1996	1.08
1997	1.11
1998	1.15
1999	1.19
2000	1.23
2001	1.27
2002	1.31
2003	1.36
2004	1.4
2005	1.45
2006	1.49
2007	1.54
2008	1.59
2009	1.64
2010	1.69
2011	1.74
2012	1.79
2013	1.85
2014	1.9
2015	1.96