Year	Years
1970	2.49
1971	2.55
1972	2.62
1973	2.68
1974	2.75
1975	2.82
1976	2.89
1977	2.96
1978	3.04
1979	3.11
1980	3.19
1981	3.26
1982	3.34
1983	3.43
1984	3.51
1985	3.59
1986	3.68
1987	3.77
1988	3.86
1989	3.95
1990	4.04
1991	4.14
1992	4.23
1993	4.33
1994	4.43
1995	4.53
1996	4.63
1997	4.74
1998	4.84
1999	4.95
2000	5.05
2001	5.16
2002	5.27
2003	5.38
2004	5.49
2005	5.61
2006	5.72
2007	5.84
2008	5.96
2009	6.08
2010	6.2
2011	6.32
2012	6.44
2013	6.56
2014	6.69
2015	6.82