Year	Years
1970	4.17
1971	4.26
1972	4.36
1973	4.45
1974	4.55
1975	4.65
1976	4.75
1977	4.86
1978	4.96
1979	5.06
1980	5.17
1981	5.28
1982	5.38
1983	5.49
1984	5.6
1985	5.71
1986	5.82
1987	5.93
1988	6.04
1989	6.15
1990	6.26
1991	6.37
1992	6.48
1993	6.59
1994	6.7
1995	6.81
1996	6.92
1997	7.03
1998	7.14
1999	7.26
2000	7.37
2001	7.49
2002	7.61
2003	7.73
2004	7.85
2005	7.97
2006	8.09
2007	8.22
2008	8.34
2009	8.47
2010	8.6
2011	8.73
2012	8.86
2013	8.99
2014	9.13
2015	9.26