Year	Years
1970	0.41
1971	0.43
1972	0.44
1973	0.46
1974	0.47
1975	0.49
1976	0.51
1977	0.52
1978	0.54
1979	0.56
1980	0.58
1981	0.6
1982	0.62
1983	0.64
1984	0.66
1985	0.68
1986	0.7
1987	0.73
1988	0.75
1989	0.78
1990	0.8
1991	0.83
1992	0.86
1993	0.88
1994	0.91
1995	0.94
1996	0.98
1997	1.01
1998	1.04
1999	1.07
2000	1.11
2001	1.14
2002	1.18
2003	1.22
2004	1.26
2005	1.3
2006	1.34
2007	1.38
2008	1.43
2009	1.47
2010	1.52
2011	1.57
2012	1.62
2013	1.67
2014	1.72
2015	1.78