Year	Years
1970	8.58
1971	8.73
1972	8.87
1973	9
1974	9.14
1975	9.27
1976	9.4
1977	9.53
1978	9.66
1979	9.78
1980	9.91
1981	10.03
1982	10.15
1983	10.26
1984	10.38
1985	10.49
1986	10.6
1987	10.71
1988	10.82
1989	10.93
1990	11.03
1991	11.13
1992	11.23
1993	11.32
1994	11.42
1995	11.51
1996	11.61
1997	11.72
1998	11.82
1999	11.93
2000	12.04
2001	12.15
2002	12.26
2003	12.38
2004	12.5
2005	12.62
2006	12.74
2007	12.87
2008	13
2009	13.13
2010	13.26
2011	13.39
2012	13.53
2013	13.67
2014	13.8
2015	13.94