Year	Years
1970	4.65
1971	4.75
1972	4.85
1973	4.95
1974	5.06
1975	5.16
1976	5.27
1977	5.37
1978	5.48
1979	5.59
1980	5.7
1981	5.82
1982	5.93
1983	6.04
1984	6.16
1985	6.27
1986	6.39
1987	6.51
1988	6.62
1989	6.74
1990	6.86
1991	6.98
1992	7.09
1993	7.21
1994	7.33
1995	7.45
1996	7.56
1997	7.67
1998	7.78
1999	7.9
2000	8.01
2001	8.13
2002	8.25
2003	8.37
2004	8.49
2005	8.62
2006	8.74
2007	8.87
2008	8.99
2009	9.12
2010	9.25
2011	9.38
2012	9.51
2013	9.64
2014	9.77
2015	9.9