Year	Years
1970	6.59
1971	6.72
1972	6.86
1973	6.99
1974	7.13
1975	7.27
1976	7.42
1977	7.56
1978	7.71
1979	7.86
1980	8.02
1981	8.17
1982	8.33
1983	8.49
1984	8.66
1985	8.83
1986	9
1987	9.17
1988	9.35
1989	9.53
1990	9.71
1991	9.9
1992	10.09
1993	10.29
1994	10.49
1995	10.7
1996	10.91
1997	11.11
1998	11.3
1999	11.49
2000	11.68
2001	11.86
2002	12.03
2003	12.2
2004	12.37
2005	12.53
2006	12.69
2007	12.85
2008	13
2009	13.15
2010	13.29
2011	13.44
2012	13.58
2013	13.71
2014	13.85
2015	13.98