Year	Years
1970	3.25
1971	3.32
1972	3.4
1973	3.48
1974	3.56
1975	3.64
1976	3.73
1977	3.81
1978	3.9
1979	3.99
1980	4.08
1981	4.17
1982	4.26
1983	4.35
1984	4.45
1985	4.55
1986	4.65
1987	4.74
1988	4.85
1989	4.95
1990	5.05
1991	5.16
1992	5.26
1993	5.37
1994	5.48
1995	5.59
1996	5.7
1997	5.81
1998	5.92
1999	6.03
2000	6.15
2001	6.27
2002	6.38
2003	6.5
2004	6.62
2005	6.75
2006	6.87
2007	7
2008	7.12
2009	7.25
2010	7.38
2011	7.51
2012	7.64
2013	7.77
2014	7.9
2015	8.04