Year	Years
1970	2.74
1971	2.82
1972	2.91
1973	2.99
1974	3.08
1975	3.17
1976	3.26
1977	3.36
1978	3.45
1979	3.55
1980	3.65
1981	3.75
1982	3.85
1983	3.95
1984	4.06
1985	4.16
1986	4.27
1987	4.38
1988	4.49
1989	4.6
1990	4.71
1991	4.82
1992	4.94
1993	5.05
1994	5.17
1995	5.28
1996	5.4
1997	5.51
1998	5.63
1999	5.75
2000	5.87
2001	5.99
2002	6.12
2003	6.24
2004	6.37
2005	6.51
2006	6.64
2007	6.78
2008	6.92
2009	7.06
2010	7.21
2011	7.35
2012	7.5
2013	7.65
2014	7.81
2015	7.96