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	3.76
1982	3.86
1983	3.97
1984	4.08
1985	4.19
1986	4.31
1987	4.42
1988	4.54
1989	4.67
1990	4.79
1991	4.92
1992	5.05
1993	5.18
1994	5.32
1995	5.46
1996	5.6
1997	5.75
1998	5.9
1999	6.05
2000	6.21
2001	6.36
2002	6.52
2003	6.67
2004	6.83
2005	6.99
2006	7.15
2007	7.31
2008	7.48
2009	7.64
2010	7.81
2011	7.97
2012	8.14
2013	8.31
2014	8.48
2015	8.64