Year	Years
1970	2.28
1971	2.33
1972	2.39
1973	2.45
1974	2.51
1975	2.57
1976	2.63
1977	2.69
1978	2.75
1979	2.82
1980	2.88
1981	2.95
1982	3.01
1983	3.08
1984	3.15
1985	3.22
1986	3.29
1987	3.36
1988	3.43
1989	3.5
1990	3.57
1991	3.65
1992	3.72
1993	3.79
1994	3.87
1995	3.94
1996	4.02
1997	4.09
1998	4.17
1999	4.25
2000	4.34
2001	4.42
2002	4.51
2003	4.6
2004	4.69
2005	4.78
2006	4.87
2007	4.97
2008	5.07
2009	5.17
2010	5.27
2011	5.38
2012	5.49
2013	5.6
2014	5.71
2015	5.82