Year	Years
1970	5.06
1971	5.16
1972	5.26
1973	5.36
1974	5.46
1975	5.56
1976	5.66
1977	5.76
1978	5.86
1979	5.97
1980	6.07
1981	6.17
1982	6.27
1983	6.37
1984	6.48
1985	6.58
1986	6.68
1987	6.78
1988	6.87
1989	6.97
1990	7.06
1991	7.16
1992	7.25
1993	7.34
1994	7.42
1995	7.51
1996	7.61
1997	7.72
1998	7.84
1999	7.95
2000	8.07
2001	8.18
2002	8.3
2003	8.42
2004	8.55
2005	8.67
2006	8.8
2007	8.93
2008	9.06
2009	9.19
2010	9.32
2011	9.45
2012	9.59
2013	9.72
2014	9.85
2015	9.99