Year	Years
1970	0.51
1971	0.54
1972	0.57
1973	0.6
1974	0.63
1975	0.66
1976	0.7
1977	0.74
1978	0.79
1979	0.83
1980	0.88
1981	0.94
1982	1
1983	1.06
1984	1.13
1985	1.2
1986	1.28
1987	1.36
1988	1.45
1989	1.54
1990	1.65
1991	1.75
1992	1.87
1993	1.99
1994	2.11
1995	2.24
1996	2.34
1997	2.43
1998	2.53
1999	2.63
2000	2.73
2001	2.83
2002	2.94
2003	3.04
2004	3.15
2005	3.25
2006	3.36
2007	3.47
2008	3.58
2009	3.7
2010	3.81
2011	3.93
2012	4.04
2013	4.16
2014	4.28
2015	4.4