Year	Years
1970	0.51
1971	0.53
1972	0.55
1973	0.57
1974	0.59
1975	0.61
1976	0.63
1977	0.65
1978	0.68
1979	0.7
1980	0.73
1981	0.75
1982	0.78
1983	0.81
1984	0.84
1985	0.87
1986	0.9
1987	0.93
1988	0.96
1989	1
1990	1.04
1991	1.07
1992	1.11
1993	1.15
1994	1.19
1995	1.24
1996	1.29
1997	1.34
1998	1.39
1999	1.44
2000	1.5
2001	1.55
2002	1.61
2003	1.67
2004	1.73
2005	1.79
2006	1.85
2007	1.92
2008	1.98
2009	2.05
2010	2.12
2011	2.19
2012	2.26
2013	2.33
2014	2.4
2015	2.48