Year	Years
1970	2.04
1971	2.09
1972	2.15
1973	2.2
1974	2.26
1975	2.32
1976	2.38
1977	2.44
1978	2.5
1979	2.56
1980	2.63
1981	2.69
1982	2.76
1983	2.83
1984	2.9
1985	2.97
1986	3.05
1987	3.12
1988	3.2
1989	3.28
1990	3.36
1991	3.44
1992	3.53
1993	3.61
1994	3.7
1995	3.79
1996	3.88
1997	3.97
1998	4.06
1999	4.16
2000	4.25
2001	4.35
2002	4.45
2003	4.55
2004	4.65
2005	4.75
2006	4.86
2007	4.96
2008	5.07
2009	5.18
2010	5.29
2011	5.4
2012	5.51
2013	5.62
2014	5.74
2015	5.85