Year	Years
1970	3.82
1971	3.9
1972	3.99
1973	4.08
1974	4.17
1975	4.26
1976	4.35
1977	4.44
1978	4.53
1979	4.63
1980	4.73
1981	4.82
1982	4.92
1983	5.02
1984	5.12
1985	5.22
1986	5.33
1987	5.43
1988	5.53
1989	5.64
1990	5.74
1991	5.85
1992	5.96
1993	6.06
1994	6.17
1995	6.28
1996	6.39
1997	6.5
1998	6.61
1999	6.73
2000	6.85
2001	6.97
2002	7.09
2003	7.21
2004	7.34
2005	7.46
2006	7.59
2007	7.72
2008	7.85
2009	7.98
2010	8.12
2011	8.25
2012	8.38
2013	8.52
2014	8.66
2015	8.8