Year	Years
1970	2.49
1971	2.56
1972	2.62
1973	2.69
1974	2.75
1975	2.82
1976	2.89
1977	2.97
1978	3.04
1979	3.12
1980	3.19
1981	3.27
1982	3.35
1983	3.43
1984	3.52
1985	3.6
1986	3.69
1987	3.78
1988	3.87
1989	3.96
1990	4.05
1991	4.15
1992	4.24
1993	4.34
1994	4.44
1995	4.54
1996	4.65
1997	4.75
1998	4.86
1999	4.97
2000	5.08
2001	5.19
2002	5.3
2003	5.41
2004	5.53
2005	5.64
2006	5.76
2007	5.88
2008	5.99
2009	6.11
2010	6.23
2011	6.36
2012	6.48
2013	6.6
2014	6.73
2015	6.85