Year	Years
1970	2.58
1971	2.65
1972	2.71
1973	2.78
1974	2.85
1975	2.92
1976	2.99
1977	3.07
1978	3.14
1979	3.22
1980	3.29
1981	3.37
1982	3.45
1983	3.54
1984	3.62
1985	3.71
1986	3.8
1987	3.88
1988	3.98
1989	4.07
1990	4.16
1991	4.26
1992	4.36
1993	4.45
1994	4.56
1995	4.66
1996	4.76
1997	4.87
1998	4.97
1999	5.08
2000	5.19
2001	5.3
2002	5.41
2003	5.53
2004	5.64
2005	5.76
2006	5.87
2007	5.99
2008	6.11
2009	6.23
2010	6.35
2011	6.48
2012	6.6
2013	6.73
2014	6.85
2015	6.98