Year	Years
1970	3.49
1971	3.59
1972	3.7
1973	3.81
1974	3.92
1975	4.03
1976	4.15
1977	4.26
1978	4.39
1979	4.51
1980	4.64
1981	4.77
1982	4.9
1983	5.03
1984	5.17
1985	5.31
1986	5.46
1987	5.6
1988	5.75
1989	5.9
1990	6.06
1991	6.21
1992	6.37
1993	6.53
1994	6.69
1995	6.86
1996	7.02
1997	7.18
1998	7.34
1999	7.5
2000	7.66
2001	7.83
2002	7.99
2003	8.16
2004	8.32
2005	8.49
2006	8.65
2007	8.82
2008	8.99
2009	9.16
2010	9.32
2011	9.49
2012	9.66
2013	9.83
2014	9.99
2015	10.16