Year	Years
1970	2.85
1971	2.92
1972	2.99
1973	3.05
1974	3.12
1975	3.19
1976	3.26
1977	3.34
1978	3.41
1979	3.48
1980	3.55
1981	3.63
1982	3.7
1983	3.77
1984	3.85
1985	3.92
1986	4
1987	4.07
1988	4.14
1989	4.22
1990	4.29
1991	4.36
1992	4.44
1993	4.51
1994	4.58
1995	4.65
1996	4.72
1997	4.79
1998	4.87
1999	4.95
2000	5.03
2001	5.11
2002	5.2
2003	5.29
2004	5.38
2005	5.47
2006	5.57
2007	5.67
2008	5.77
2009	5.87
2010	5.98
2011	6.08
2012	6.19
2013	6.31
2014	6.42
2015	6.53