Year	Years
1970	2.82
1971	2.9
1972	2.99
1973	3.07
1974	3.16
1975	3.25
1976	3.34
1977	3.44
1978	3.53
1979	3.63
1980	3.73
1981	3.84
1982	3.94
1983	4.05
1984	4.15
1985	4.27
1986	4.38
1987	4.49
1988	4.61
1989	4.73
1990	4.85
1991	4.97
1992	5.1
1993	5.22
1994	5.35
1995	5.48
1996	5.61
1997	5.74
1998	5.87
1999	6
2000	6.14
2001	6.28
2002	6.42
2003	6.56
2004	6.71
2005	6.85
2006	7
2007	7.15
2008	7.3
2009	7.46
2010	7.61
2011	7.77
2012	7.92
2013	8.08
2014	8.24
2015	8.4