Year	Years
1970	2.43
1971	2.49
1972	2.55
1973	2.61
1974	2.67
1975	2.74
1976	2.81
1977	2.88
1978	2.94
1979	3.02
1980	3.09
1981	3.16
1982	3.24
1983	3.31
1984	3.39
1985	3.47
1986	3.55
1987	3.64
1988	3.72
1989	3.8
1990	3.89
1991	3.98
1992	4.07
1993	4.16
1994	4.26
1995	4.35
1996	4.45
1997	4.55
1998	4.65
1999	4.75
2000	4.85
2001	4.95
2002	5.06
2003	5.17
2004	5.28
2005	5.39
2006	5.5
2007	5.61
2008	5.73
2009	5.84
2010	5.96
2011	6.08
2012	6.2
2013	6.32
2014	6.44
2015	6.57