Year	Years
1970	2.11
1971	2.16
1972	2.22
1973	2.27
1974	2.33
1975	2.39
1976	2.45
1977	2.51
1978	2.57
1979	2.63
1980	2.69
1981	2.76
1982	2.83
1983	2.89
1984	2.96
1985	3.03
1986	3.1
1987	3.18
1988	3.25
1989	3.32
1990	3.4
1991	3.48
1992	3.55
1993	3.63
1994	3.71
1995	3.79
1996	3.87
1997	3.95
1998	4.04
1999	4.12
2000	4.21
2001	4.29
2002	4.38
2003	4.47
2004	4.57
2005	4.66
2006	4.75
2007	4.85
2008	4.95
2009	5.05
2010	5.15
2011	5.26
2012	5.37
2013	5.47
2014	5.58
2015	5.7