Year	Years
1970	2.62
1971	2.68
1972	2.74
1973	2.81
1974	2.87
1975	2.93
1976	2.99
1977	3.05
1978	3.11
1979	3.16
1980	3.22
1981	3.28
1982	3.33
1983	3.39
1984	3.44
1985	3.5
1986	3.55
1987	3.6
1988	3.65
1989	3.7
1990	3.75
1991	3.8
1992	3.84
1993	3.89
1994	3.94
1995	3.98
1996	4.06
1997	4.14
1998	4.22
1999	4.31
2000	4.4
2001	4.49
2002	4.59
2003	4.69
2004	4.79
2005	4.89
2006	5
2007	5.11
2008	5.22
2009	5.34
2010	5.46
2011	5.58
2012	5.7
2013	5.82
2014	5.95
2015	6.08