Year	Years
1970	3.16
1971	3.25
1972	3.34
1973	3.44
1974	3.54
1975	3.63
1976	3.74
1977	3.84
1978	3.94
1979	4.05
1980	4.16
1981	4.27
1982	4.39
1983	4.5
1984	4.62
1985	4.74
1986	4.86
1987	4.99
1988	5.11
1989	5.24
1990	5.37
1991	5.51
1992	5.64
1993	5.78
1994	5.92
1995	6.06
1996	6.2
1997	6.34
1998	6.49
1999	6.64
2000	6.79
2001	6.94
2002	7.09
2003	7.25
2004	7.4
2005	7.56
2006	7.72
2007	7.88
2008	8.04
2009	8.2
2010	8.36
2011	8.52
2012	8.69
2013	8.85
2014	9.02
2015	9.18