Year	Years
1970	2.63
1971	2.7
1972	2.76
1973	2.83
1974	2.89
1975	2.96
1976	3.03
1977	3.09
1978	3.16
1979	3.23
1980	3.31
1981	3.38
1982	3.45
1983	3.53
1984	3.6
1985	3.68
1986	3.75
1987	3.83
1988	3.91
1989	3.99
1990	4.07
1991	4.15
1992	4.23
1993	4.32
1994	4.4
1995	4.49
1996	4.58
1997	4.68
1998	4.78
1999	4.87
2000	4.97
2001	5.07
2002	5.18
2003	5.28
2004	5.39
2005	5.49
2006	5.6
2007	5.71
2008	5.82
2009	5.93
2010	6.05
2011	6.16
2012	6.28
2013	6.39
2014	6.51
2015	6.63