Year	Years
1970	2.83
1971	2.9
1972	2.97
1973	3.04
1974	3.1
1975	3.17
1976	3.25
1977	3.32
1978	3.39
1979	3.47
1980	3.54
1981	3.62
1982	3.7
1983	3.77
1984	3.85
1985	3.93
1986	4.02
1987	4.1
1988	4.18
1989	4.26
1990	4.35
1991	4.43
1992	4.52
1993	4.6
1994	4.69
1995	4.78
1996	4.87
1997	4.95
1998	5.05
1999	5.14
2000	5.23
2001	5.33
2002	5.43
2003	5.53
2004	5.63
2005	5.73
2006	5.84
2007	5.94
2008	6.05
2009	6.16
2010	6.27
2011	6.38
2012	6.5
2013	6.61
2014	6.73
2015	6.85