Year	Years
1970	2.77
1971	2.84
1972	2.91
1973	2.98
1974	3.05
1975	3.13
1976	3.2
1977	3.28
1978	3.36
1979	3.43
1980	3.51
1981	3.6
1982	3.68
1983	3.76
1984	3.85
1985	3.94
1986	4.03
1987	4.12
1988	4.21
1989	4.3
1990	4.4
1991	4.49
1992	4.59
1993	4.69
1994	4.79
1995	4.89
1996	5
1997	5.1
1998	5.21
1999	5.32
2000	5.43
2001	5.55
2002	5.66
2003	5.77
2004	5.89
2005	6.01
2006	6.13
2007	6.25
2008	6.37
2009	6.5
2010	6.62
2011	6.75
2012	6.87
2013	7
2014	7.13
2015	7.26