Year	Years
1970	0.37
1971	0.39
1972	0.41
1973	0.42
1974	0.44
1975	0.47
1976	0.49
1977	0.51
1978	0.54
1979	0.57
1980	0.6
1981	0.63
1982	0.67
1983	0.7
1984	0.74
1985	0.79
1986	0.84
1987	0.89
1988	0.94
1989	1
1990	1.07
1991	1.14
1992	1.23
1993	1.31
1994	1.41
1995	1.52
1996	1.61
1997	1.7
1998	1.8
1999	1.89
2000	1.99
2001	2.09
2002	2.2
2003	2.3
2004	2.41
2005	2.51
2006	2.62
2007	2.73
2008	2.84
2009	2.95
2010	3.06
2011	3.17
2012	3.27
2013	3.38
2014	3.49
2015	3.6