Year	Years
1970	4.45
1971	4.55
1972	4.65
1973	4.75
1974	4.85
1975	4.95
1976	5.06
1977	5.16
1978	5.27
1979	5.38
1980	5.49
1981	5.6
1982	5.71
1983	5.82
1984	5.94
1985	6.05
1986	6.17
1987	6.28
1988	6.4
1989	6.52
1990	6.64
1991	6.76
1992	6.88
1993	7
1994	7.12
1995	7.24
1996	7.36
1997	7.48
1998	7.6
1999	7.72
2000	7.84
2001	7.97
2002	8.09
2003	8.22
2004	8.35
2005	8.48
2006	8.61
2007	8.74
2008	8.87
2009	9.01
2010	9.14
2011	9.28
2012	9.41
2013	9.55
2014	9.69
2015	9.83