Year	Years
1970	2.23
1971	2.29
1972	2.35
1973	2.41
1974	2.47
1975	2.54
1976	2.61
1977	2.68
1978	2.75
1979	2.82
1980	2.89
1981	2.97
1982	3.05
1983	3.13
1984	3.21
1985	3.3
1986	3.38
1987	3.47
1988	3.57
1989	3.66
1990	3.75
1991	3.85
1992	3.95
1993	4.06
1994	4.16
1995	4.27
1996	4.37
1997	4.47
1998	4.57
1999	4.68
2000	4.78
2001	4.89
2002	4.99
2003	5.1
2004	5.21
2005	5.32
2006	5.43
2007	5.54
2008	5.66
2009	5.77
2010	5.89
2011	6.01
2012	6.13
2013	6.25
2014	6.37
2015	6.49