Year	Years
1970	2.79
1971	2.88
1972	2.97
1973	3.05
1974	3.15
1975	3.24
1976	3.33
1977	3.43
1978	3.53
1979	3.64
1980	3.74
1981	3.85
1982	3.96
1983	4.07
1984	4.19
1985	4.31
1986	4.43
1987	4.56
1988	4.68
1989	4.81
1990	4.94
1991	5.08
1992	5.22
1993	5.36
1994	5.5
1995	5.65
1996	5.79
1997	5.94
1998	6.09
1999	6.24
2000	6.39
2001	6.54
2002	6.69
2003	6.85
2004	7.01
2005	7.16
2006	7.32
2007	7.48
2008	7.64
2009	7.81
2010	7.97
2011	8.13
2012	8.3
2013	8.46
2014	8.63
2015	8.79