Year	Years
1970	3.79
1971	3.88
1972	3.97
1973	4.06
1974	4.15
1975	4.25
1976	4.34
1977	4.44
1978	4.54
1979	4.64
1980	4.74
1981	4.85
1982	4.95
1983	5.06
1984	5.17
1985	5.27
1986	5.38
1987	5.5
1988	5.61
1989	5.72
1990	5.84
1991	5.95
1992	6.07
1993	6.19
1994	6.31
1995	6.43
1996	6.54
1997	6.66
1998	6.78
1999	6.9
2000	7.02
2001	7.15
2002	7.27
2003	7.39
2004	7.52
2005	7.64
2006	7.77
2007	7.9
2008	8.03
2009	8.15
2010	8.28
2011	8.41
2012	8.55
2013	8.68
2014	8.81
2015	8.94