Year	Years
1970	2.66
1971	2.74
1972	2.82
1973	2.9
1974	2.98
1975	3.07
1976	3.16
1977	3.25
1978	3.34
1979	3.44
1980	3.53
1981	3.63
1982	3.73
1983	3.84
1984	3.94
1985	4.05
1986	4.16
1987	4.27
1988	4.38
1989	4.5
1990	4.62
1991	4.74
1992	4.86
1993	4.99
1994	5.11
1995	5.24
1996	5.37
1997	5.5
1998	5.64
1999	5.78
2000	5.91
2001	6.06
2002	6.2
2003	6.34
2004	6.49
2005	6.64
2006	6.79
2007	6.94
2008	7.09
2009	7.25
2010	7.41
2011	7.56
2012	7.72
2013	7.88
2014	8.05
2015	8.21