Year	Years
1970	4.39
1971	4.48
1972	4.58
1973	4.68
1974	4.78
1975	4.89
1976	4.99
1977	5.1
1978	5.21
1979	5.32
1980	5.43
1981	5.54
1982	5.65
1983	5.77
1984	5.88
1985	6
1986	6.12
1987	6.24
1988	6.36
1989	6.49
1990	6.61
1991	6.74
1992	6.86
1993	6.99
1994	7.12
1995	7.25
1996	7.38
1997	7.52
1998	7.65
1999	7.79
2000	7.92
2001	8.06
2002	8.19
2003	8.33
2004	8.47
2005	8.61
2006	8.75
2007	8.89
2008	9.03
2009	9.17
2010	9.31
2011	9.45
2012	9.59
2013	9.73
2014	9.87
2015	10.01