Year	Years
1970	3.1
1971	3.19
1972	3.28
1973	3.37
1974	3.47
1975	3.56
1976	3.66
1977	3.76
1978	3.87
1979	3.97
1980	4.08
1981	4.19
1982	4.3
1983	4.41
1984	4.52
1985	4.64
1986	4.76
1987	4.88
1988	5.01
1989	5.13
1990	5.26
1991	5.39
1992	5.52
1993	5.66
1994	5.79
1995	5.93
1996	6.07
1997	6.21
1998	6.36
1999	6.5
2000	6.65
2001	6.8
2002	6.95
2003	7.11
2004	7.26
2005	7.42
2006	7.58
2007	7.74
2008	7.9
2009	8.06
2010	8.22
2011	8.39
2012	8.55
2013	8.72
2014	8.88
2015	9.05