Year	Years
1970	2.82
1971	2.89
1972	2.95
1973	3.02
1974	3.09
1975	3.15
1976	3.22
1977	3.29
1978	3.36
1979	3.44
1980	3.51
1981	3.58
1982	3.66
1983	3.73
1984	3.81
1985	3.88
1986	3.96
1987	4.03
1988	4.11
1989	4.19
1990	4.27
1991	4.35
1992	4.43
1993	4.51
1994	4.59
1995	4.67
1996	4.76
1997	4.85
1998	4.95
1999	5.04
2000	5.14
2001	5.24
2002	5.34
2003	5.45
2004	5.55
2005	5.66
2006	5.77
2007	5.88
2008	5.99
2009	6.1
2010	6.22
2011	6.33
2012	6.45
2013	6.57
2014	6.69
2015	6.81