Year	Years
1970	4.65
1971	4.75
1972	4.85
1973	4.96
1974	5.06
1975	5.16
1976	5.27
1977	5.37
1978	5.47
1979	5.57
1980	5.68
1981	5.78
1982	5.88
1983	5.98
1984	6.08
1985	6.18
1986	6.28
1987	6.38
1988	6.48
1989	6.58
1990	6.67
1991	6.77
1992	6.87
1993	6.97
1994	7.06
1995	7.16
1996	7.29
1997	7.43
1998	7.56
1999	7.7
2000	7.85
2001	7.99
2002	8.14
2003	8.29
2004	8.44
2005	8.59
2006	8.74
2007	8.9
2008	9.05
2009	9.21
2010	9.37
2011	9.53
2012	9.69
2013	9.85
2014	10.01
2015	10.18