Year	Years
1970	2.59
1971	2.65
1972	2.72
1973	2.78
1974	2.85
1975	2.92
1976	2.99
1977	3.06
1978	3.14
1979	3.21
1980	3.29
1981	3.36
1982	3.44
1983	3.52
1984	3.6
1985	3.69
1986	3.77
1987	3.86
1988	3.94
1989	4.03
1990	4.12
1991	4.22
1992	4.31
1993	4.4
1994	4.5
1995	4.6
1996	4.7
1997	4.8
1998	4.9
1999	5.01
2000	5.12
2001	5.22
2002	5.33
2003	5.44
2004	5.56
2005	5.67
2006	5.79
2007	5.9
2008	6.02
2009	6.14
2010	6.26
2011	6.38
2012	6.51
2013	6.63
2014	6.76
2015	6.89