Year	Years
1970	1.89
1971	1.95
1972	2
1973	2.06
1974	2.12
1975	2.18
1976	2.25
1977	2.31
1978	2.38
1979	2.44
1980	2.51
1981	2.58
1982	2.65
1983	2.72
1984	2.79
1985	2.86
1986	2.94
1987	3.01
1988	3.09
1989	3.16
1990	3.24
1991	3.32
1992	3.4
1993	3.48
1994	3.56
1995	3.64
1996	3.72
1997	3.81
1998	3.9
1999	3.99
2000	4.08
2001	4.17
2002	4.27
2003	4.37
2004	4.47
2005	4.57
2006	4.68
2007	4.78
2008	4.89
2009	5
2010	5.12
2011	5.24
2012	5.36
2013	5.48
2014	5.6
2015	5.73