Year	Years
1970	6.05
1971	6.15
1972	6.25
1973	6.35
1974	6.45
1975	6.54
1976	6.64
1977	6.73
1978	6.83
1979	6.92
1980	7.01
1981	7.1
1982	7.18
1983	7.27
1984	7.35
1985	7.42
1986	7.49
1987	7.56
1988	7.62
1989	7.67
1990	7.72
1991	7.77
1992	7.8
1993	7.83
1994	7.86
1995	7.88
1996	7.97
1997	8.07
1998	8.17
1999	8.28
2000	8.39
2001	8.5
2002	8.61
2003	8.73
2004	8.85
2005	8.97
2006	9.1
2007	9.22
2008	9.35
2009	9.48
2010	9.61
2011	9.74
2012	9.87
2013	10
2014	10.13
2015	10.27