Year	Years
1970	2.44
1971	2.5
1972	2.56
1973	2.63
1974	2.69
1975	2.76
1976	2.83
1977	2.9
1978	2.98
1979	3.05
1980	3.13
1981	3.2
1982	3.28
1983	3.36
1984	3.44
1985	3.53
1986	3.61
1987	3.7
1988	3.79
1989	3.88
1990	3.97
1991	4.06
1992	4.16
1993	4.25
1994	4.35
1995	4.45
1996	4.55
1997	4.66
1998	4.76
1999	4.86
2000	4.97
2001	5.08
2002	5.19
2003	5.3
2004	5.41
2005	5.52
2006	5.63
2007	5.75
2008	5.86
2009	5.98
2010	6.1
2011	6.21
2012	6.33
2013	6.45
2014	6.58
2015	6.7