Year	Years
1970	2.08
1971	2.14
1972	2.21
1973	2.28
1974	2.35
1975	2.42
1976	2.49
1977	2.57
1978	2.65
1979	2.73
1980	2.81
1981	2.9
1982	2.99
1983	3.08
1984	3.17
1985	3.26
1986	3.36
1987	3.46
1988	3.57
1989	3.67
1990	3.78
1991	3.89
1992	4.01
1993	4.13
1994	4.25
1995	4.37
1996	4.5
1997	4.64
1998	4.77
1999	4.91
2000	5.04
2001	5.18
2002	5.32
2003	5.47
2004	5.61
2005	5.76
2006	5.91
2007	6.06
2008	6.21
2009	6.36
2010	6.52
2011	6.67
2012	6.83
2013	6.99
2014	7.15
2015	7.31