Year	Years
1970	3.05
1971	3.14
1972	3.23
1973	3.32
1974	3.42
1975	3.51
1976	3.61
1977	3.71
1978	3.81
1979	3.92
1980	4.02
1981	4.13
1982	4.24
1983	4.35
1984	4.47
1985	4.58
1986	4.7
1987	4.82
1988	4.95
1989	5.07
1990	5.2
1991	5.32
1992	5.45
1993	5.59
1994	5.72
1995	5.86
1996	5.99
1997	6.13
1998	6.28
1999	6.42
2000	6.57
2001	6.71
2002	6.86
2003	7.01
2004	7.17
2005	7.32
2006	7.48
2007	7.63
2008	7.79
2009	7.95
2010	8.12
2011	8.28
2012	8.44
2013	8.61
2014	8.78
2015	8.94