Year	Years
1970	7.52
1971	7.66
1972	7.79
1973	7.93
1974	8.07
1975	8.21
1976	8.34
1977	8.48
1978	8.62
1979	8.76
1980	8.9
1981	9.04
1982	9.18
1983	9.32
1984	9.46
1985	9.59
1986	9.73
1987	9.87
1988	10
1989	10.14
1990	10.27
1991	10.4
1992	10.54
1993	10.67
1994	10.8
1995	10.92
1996	11.05
1997	11.18
1998	11.3
1999	11.42
2000	11.55
2001	11.67
2002	11.8
2003	11.92
2004	12.04
2005	12.16
2006	12.29
2007	12.41
2008	12.53
2009	12.65
2010	12.77
2011	12.89
2012	13.01
2013	13.13
2014	13.25
2015	13.36