Year	Years
1970	2.97
1971	3.04
1972	3.1
1973	3.17
1974	3.25
1975	3.32
1976	3.39
1977	3.47
1978	3.54
1979	3.62
1980	3.69
1981	3.77
1982	3.85
1983	3.92
1984	4
1985	4.08
1986	4.16
1987	4.24
1988	4.32
1989	4.4
1990	4.47
1991	4.55
1992	4.63
1993	4.7
1994	4.78
1995	4.85
1996	4.92
1997	5
1998	5.08
1999	5.16
2000	5.25
2001	5.33
2002	5.42
2003	5.51
2004	5.61
2005	5.71
2006	5.8
2007	5.9
2008	6.01
2009	6.11
2010	6.22
2011	6.32
2012	6.43
2013	6.54
2014	6.65
2015	6.77