Year	Years
1970	7.77
1971	7.92
1972	8.08
1973	8.23
1974	8.38
1975	8.54
1976	8.69
1977	8.84
1978	8.98
1979	9.13
1980	9.28
1981	9.42
1982	9.56
1983	9.7
1984	9.84
1985	9.98
1986	10.12
1987	10.26
1988	10.39
1989	10.53
1990	10.66
1991	10.8
1992	10.93
1993	11.07
1994	11.2
1995	11.33
1996	11.48
1997	11.63
1998	11.77
1999	11.93
2000	12.08
2001	12.23
2002	12.38
2003	12.54
2004	12.69
2005	12.85
2006	13
2007	13.15
2008	13.31
2009	13.46
2010	13.61
2011	13.76
2012	13.9
2013	14.05
2014	14.19
2015	14.34