Year	Years
1970	0.33
1971	0.35
1972	0.36
1973	0.37
1974	0.38
1975	0.4
1976	0.41
1977	0.43
1978	0.44
1979	0.46
1980	0.47
1981	0.49
1982	0.51
1983	0.53
1984	0.54
1985	0.56
1986	0.58
1987	0.61
1988	0.63
1989	0.65
1990	0.67
1991	0.7
1992	0.72
1993	0.75
1994	0.78
1995	0.81
1996	0.84
1997	0.87
1998	0.9
1999	0.93
2000	0.96
2001	1
2002	1.03
2003	1.07
2004	1.11
2005	1.14
2006	1.18
2007	1.22
2008	1.26
2009	1.3
2010	1.35
2011	1.39
2012	1.43
2013	1.48
2014	1.53
2015	1.57