Year	Years
1970	2.02
1971	2.08
1972	2.15
1973	2.21
1974	2.28
1975	2.35
1976	2.42
1977	2.49
1978	2.57
1979	2.65
1980	2.72
1981	2.81
1982	2.89
1983	2.97
1984	3.06
1985	3.15
1986	3.24
1987	3.33
1988	3.43
1989	3.52
1990	3.62
1991	3.73
1992	3.83
1993	3.94
1994	4.04
1995	4.16
1996	4.27
1997	4.38
1998	4.5
1999	4.62
2000	4.74
2001	4.87
2002	4.99
2003	5.12
2004	5.25
2005	5.38
2006	5.52
2007	5.66
2008	5.79
2009	5.94
2010	6.08
2011	6.22
2012	6.37
2013	6.52
2014	6.67
2015	6.82