Year	Years
1970	2.45
1971	2.52
1972	2.58
1973	2.64
1974	2.71
1975	2.78
1976	2.85
1977	2.92
1978	2.99
1979	3.07
1980	3.14
1981	3.22
1982	3.3
1983	3.38
1984	3.46
1985	3.54
1986	3.63
1987	3.72
1988	3.8
1989	3.9
1990	3.99
1991	4.08
1992	4.18
1993	4.27
1994	4.37
1995	4.47
1996	4.58
1997	4.68
1998	4.79
1999	4.89
2000	5
2001	5.11
2002	5.22
2003	5.33
2004	5.44
2005	5.55
2006	5.66
2007	5.78
2008	5.89
2009	6.01
2010	6.12
2011	6.24
2012	6.36
2013	6.48
2014	6.6
2015	6.73