Year	Years
1970	2.57
1971	2.65
1972	2.73
1973	2.81
1974	2.9
1975	2.98
1976	3.07
1977	3.16
1978	3.26
1979	3.35
1980	3.45
1981	3.55
1982	3.65
1983	3.76
1984	3.87
1985	3.98
1986	4.09
1987	4.2
1988	4.32
1989	4.44
1990	4.56
1991	4.68
1992	4.81
1993	4.94
1994	5.07
1995	5.2
1996	5.34
1997	5.47
1998	5.61
1999	5.75
2000	5.89
2001	6.03
2002	6.18
2003	6.32
2004	6.47
2005	6.62
2006	6.77
2007	6.92
2008	7.08
2009	7.23
2010	7.39
2011	7.55
2012	7.71
2013	7.87
2014	8.03
2015	8.19