Year	Years
1970	0.31
1971	0.33
1972	0.34
1973	0.35
1974	0.37
1975	0.39
1976	0.4
1977	0.42
1978	0.44
1979	0.46
1980	0.48
1981	0.51
1982	0.53
1983	0.56
1984	0.58
1985	0.61
1986	0.65
1987	0.68
1988	0.71
1989	0.75
1990	0.79
1991	0.84
1992	0.88
1993	0.93
1994	0.98
1995	1.04
1996	1.09
1997	1.15
1998	1.21
1999	1.27
2000	1.32
2001	1.38
2002	1.45
2003	1.51
2004	1.57
2005	1.64
2006	1.7
2007	1.77
2008	1.84
2009	1.91
2010	1.98
2011	2.05
2012	2.12
2013	2.2
2014	2.27
2015	2.35