Year	Years
1970	2.88
1971	2.97
1972	3.05
1973	3.14
1974	3.23
1975	3.32
1976	3.42
1977	3.52
1978	3.61
1979	3.71
1980	3.82
1981	3.92
1982	4.03
1983	4.14
1984	4.25
1985	4.36
1986	4.48
1987	4.6
1988	4.72
1989	4.84
1990	4.97
1991	5.09
1992	5.22
1993	5.35
1994	5.48
1995	5.62
1996	5.75
1997	5.89
1998	6.03
1999	6.17
2000	6.32
2001	6.46
2002	6.61
2003	6.76
2004	6.91
2005	7.06
2006	7.22
2007	7.37
2008	7.53
2009	7.69
2010	7.85
2011	8
2012	8.17
2013	8.33
2014	8.49
2015	8.65