Year	Years
1970	5.62
1971	5.73
1972	5.83
1973	5.93
1974	6.03
1975	6.13
1976	6.23
1977	6.33
1978	6.43
1979	6.53
1980	6.63
1981	6.72
1982	6.81
1983	6.9
1984	6.99
1985	7.08
1986	7.17
1987	7.25
1988	7.33
1989	7.4
1990	7.48
1991	7.55
1992	7.61
1993	7.67
1994	7.73
1995	7.77
1996	7.83
1997	7.89
1998	7.96
1999	8.04
2000	8.11
2001	8.2
2002	8.28
2003	8.38
2004	8.47
2005	8.57
2006	8.67
2007	8.78
2008	8.88
2009	9
2010	9.11
2011	9.22
2012	9.34
2013	9.46
2014	9.59
2015	9.71