Year	Years
1970	2.49
1971	2.57
1972	2.66
1973	2.75
1974	2.84
1975	2.94
1976	3.04
1977	3.15
1978	3.25
1979	3.37
1980	3.48
1981	3.6
1982	3.72
1983	3.85
1984	3.98
1985	4.12
1986	4.26
1987	4.4
1988	4.55
1989	4.7
1990	4.86
1991	5.02
1992	5.19
1993	5.36
1994	5.54
1995	5.72
1996	5.89
1997	6.06
1998	6.22
1999	6.39
2000	6.56
2001	6.73
2002	6.89
2003	7.06
2004	7.23
2005	7.4
2006	7.56
2007	7.73
2008	7.9
2009	8.06
2010	8.23
2011	8.4
2012	8.56
2013	8.73
2014	8.89
2015	9.06