Year	Years
1970	4.55
1971	4.65
1972	4.75
1973	4.85
1974	4.95
1975	5.05
1976	5.15
1977	5.25
1978	5.36
1979	5.46
1980	5.57
1981	5.67
1982	5.78
1983	5.89
1984	5.99
1985	6.1
1986	6.21
1987	6.32
1988	6.43
1989	6.54
1990	6.65
1991	6.76
1992	6.87
1993	6.98
1994	7.09
1995	7.2
1996	7.32
1997	7.45
1998	7.57
1999	7.7
2000	7.83
2001	7.95
2002	8.08
2003	8.21
2004	8.34
2005	8.48
2006	8.61
2007	8.74
2008	8.88
2009	9.01
2010	9.15
2011	9.28
2012	9.42
2013	9.55
2014	9.69
2015	9.83