Year	Years
1970	2.09
1971	2.15
1972	2.2
1973	2.26
1974	2.32
1975	2.38
1976	2.44
1977	2.5
1978	2.57
1979	2.63
1980	2.7
1981	2.77
1982	2.84
1983	2.91
1984	2.99
1985	3.07
1986	3.15
1987	3.23
1988	3.31
1989	3.4
1990	3.49
1991	3.58
1992	3.68
1993	3.78
1994	3.88
1995	3.99
1996	4.1
1997	4.21
1998	4.33
1999	4.44
2000	4.55
2001	4.67
2002	4.78
2003	4.9
2004	5.02
2005	5.13
2006	5.25
2007	5.37
2008	5.49
2009	5.61
2010	5.74
2011	5.86
2012	5.99
2013	6.11
2014	6.24
2015	6.37