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	0.67
1979	0.7
1980	0.72
1981	0.75
1982	0.77
1983	0.8
1984	0.83
1985	0.86
1986	0.89
1987	0.92
1988	0.95
1989	0.99
1990	1.02
1991	1.06
1992	1.1
1993	1.13
1994	1.18
1995	1.22
1996	1.26
1997	1.31
1998	1.36
1999	1.4
2000	1.45
2001	1.5
2002	1.56
2003	1.61
2004	1.66
2005	1.72
2006	1.78
2007	1.84
2008	1.9
2009	1.96
2010	2.02
2011	2.09
2012	2.15
2013	2.22
2014	2.29
2015	2.36