Year	Years
1970	2.09
1971	2.15
1972	2.21
1973	2.28
1974	2.35
1975	2.42
1976	2.49
1977	2.57
1978	2.64
1979	2.72
1980	2.8
1981	2.88
1982	2.97
1983	3.05
1984	3.14
1985	3.23
1986	3.32
1987	3.42
1988	3.51
1989	3.61
1990	3.71
1991	3.81
1992	3.91
1993	4.02
1994	4.13
1995	4.24
1996	4.35
1997	4.46
1998	4.58
1999	4.7
2000	4.82
2001	4.94
2002	5.06
2003	5.19
2004	5.32
2005	5.45
2006	5.58
2007	5.72
2008	5.85
2009	5.99
2010	6.13
2011	6.28
2012	6.42
2013	6.57
2014	6.72
2015	6.87