Year	Years
1970	6.21
1971	6.31
1972	6.42
1973	6.53
1974	6.63
1975	6.74
1976	6.84
1977	6.94
1978	7.05
1979	7.15
1980	7.25
1981	7.34
1982	7.44
1983	7.53
1984	7.62
1985	7.71
1986	7.8
1987	7.88
1988	7.96
1989	8.04
1990	8.11
1991	8.18
1992	8.25
1993	8.31
1994	8.37
1995	8.42
1996	8.49
1997	8.56
1998	8.63
1999	8.71
2000	8.8
2001	8.89
2002	8.98
2003	9.08
2004	9.17
2005	9.28
2006	9.38
2007	9.49
2008	9.6
2009	9.71
2010	9.82
2011	9.94
2012	10.06
2013	10.18
2014	10.31
2015	10.43