Year	Years
1970	2.86
1971	2.95
1972	3.04
1973	3.13
1974	3.23
1975	3.32
1976	3.42
1977	3.53
1978	3.63
1979	3.74
1980	3.85
1981	3.96
1982	4.08
1983	4.2
1984	4.32
1985	4.44
1986	4.57
1987	4.69
1988	4.82
1989	4.95
1990	5.09
1991	5.22
1992	5.36
1993	5.5
1994	5.64
1995	5.78
1996	5.92
1997	6.06
1998	6.21
1999	6.35
2000	6.5
2001	6.64
2002	6.79
2003	6.95
2004	7.1
2005	7.25
2006	7.41
2007	7.57
2008	7.73
2009	7.89
2010	8.05
2011	8.21
2012	8.37
2013	8.54
2014	8.7
2015	8.87