Year	Years
1970	0.45
1971	0.46
1972	0.48
1973	0.49
1974	0.51
1975	0.52
1976	0.54
1977	0.55
1978	0.57
1979	0.59
1980	0.61
1981	0.62
1982	0.64
1983	0.66
1984	0.69
1985	0.71
1986	0.73
1987	0.75
1988	0.78
1989	0.8
1990	0.83
1991	0.86
1992	0.89
1993	0.92
1994	0.95
1995	0.98
1996	1.02
1997	1.06
1998	1.11
1999	1.15
2000	1.19
2001	1.24
2002	1.28
2003	1.33
2004	1.37
2005	1.42
2006	1.47
2007	1.52
2008	1.57
2009	1.62
2010	1.67
2011	1.72
2012	1.77
2013	1.83
2014	1.88
2015	1.93