Year	Years
1970	2.61
1971	2.66
1972	2.72
1973	2.78
1974	2.83
1975	2.89
1976	2.95
1977	3
1978	3.06
1979	3.12
1980	3.17
1981	3.23
1982	3.28
1983	3.34
1984	3.4
1985	3.45
1986	3.51
1987	3.57
1988	3.64
1989	3.7
1990	3.78
1991	3.85
1992	3.94
1993	4.03
1994	4.12
1995	4.23
1996	4.35
1997	4.47
1998	4.59
1999	4.72
2000	4.84
2001	4.97
2002	5.1
2003	5.24
2004	5.37
2005	5.51
2006	5.65
2007	5.79
2008	5.94
2009	6.08
2010	6.23
2011	6.38
2012	6.53
2013	6.68
2014	6.83
2015	6.99