Year	Years
1970	0.31
1971	0.32
1972	0.33
1973	0.34
1974	0.35
1975	0.37
1976	0.38
1977	0.4
1978	0.41
1979	0.43
1980	0.44
1981	0.46
1982	0.47
1983	0.49
1984	0.51
1985	0.53
1986	0.55
1987	0.57
1988	0.59
1989	0.62
1990	0.64
1991	0.66
1992	0.69
1993	0.72
1994	0.75
1995	0.77
1996	0.81
1997	0.84
1998	0.87
1999	0.91
2000	0.94
2001	0.98
2002	1.01
2003	1.05
2004	1.09
2005	1.13
2006	1.17
2007	1.21
2008	1.25
2009	1.29
2010	1.34
2011	1.38
2012	1.43
2013	1.48
2014	1.53
2015	1.57