Year	Years
1970	6.39
1971	6.53
1972	6.68
1973	6.82
1974	6.97
1975	7.11
1976	7.26
1977	7.41
1978	7.55
1979	7.7
1980	7.84
1981	7.99
1982	8.14
1983	8.28
1984	8.42
1985	8.57
1986	8.71
1987	8.85
1988	8.99
1989	9.13
1990	9.27
1991	9.41
1992	9.55
1993	9.69
1994	9.83
1995	9.97
1996	10.12
1997	10.27
1998	10.42
1999	10.57
2000	10.73
2001	10.89
2002	11.05
2003	11.21
2004	11.37
2005	11.54
2006	11.7
2007	11.87
2008	12.03
2009	12.2
2010	12.36
2011	12.53
2012	12.69
2013	12.85
2014	13.01
2015	13.17