Year	Years
1970	4.41
1971	4.51
1972	4.61
1973	4.71
1974	4.81
1975	4.91
1976	5.01
1977	5.12
1978	5.22
1979	5.33
1980	5.44
1981	5.55
1982	5.66
1983	5.77
1984	5.89
1985	6
1986	6.12
1987	6.23
1988	6.35
1989	6.47
1990	6.59
1991	6.71
1992	6.83
1993	6.96
1994	7.08
1995	7.21
1996	7.33
1997	7.45
1998	7.58
1999	7.7
2000	7.83
2001	7.96
2002	8.09
2003	8.22
2004	8.35
2005	8.48
2006	8.61
2007	8.75
2008	8.88
2009	9.02
2010	9.15
2011	9.29
2012	9.43
2013	9.56
2014	9.7
2015	9.84