Year	Years
1970	0.38
1971	0.39
1972	0.4
1973	0.41
1974	0.43
1975	0.44
1976	0.46
1977	0.47
1978	0.49
1979	0.5
1980	0.52
1981	0.54
1982	0.56
1983	0.58
1984	0.59
1985	0.61
1986	0.64
1987	0.66
1988	0.68
1989	0.7
1990	0.72
1991	0.75
1992	0.77
1993	0.8
1994	0.82
1995	0.85
1996	0.88
1997	0.91
1998	0.94
1999	0.97
2000	1
2001	1.03
2002	1.06
2003	1.1
2004	1.13
2005	1.17
2006	1.21
2007	1.25
2008	1.29
2009	1.33
2010	1.37
2011	1.41
2012	1.46
2013	1.51
2014	1.55
2015	1.6