Year	Years
1970	2.84
1971	2.95
1972	3.05
1973	3.17
1974	3.28
1975	3.41
1976	3.54
1977	3.67
1978	3.81
1979	3.95
1980	4.1
1981	4.26
1982	4.43
1983	4.6
1984	4.77
1985	4.96
1986	5.15
1987	5.35
1988	5.55
1989	5.76
1990	5.97
1991	6.19
1992	6.42
1993	6.64
1994	6.86
1995	7.08
1996	7.24
1997	7.4
1998	7.55
1999	7.7
2000	7.85
2001	8
2002	8.15
2003	8.29
2004	8.44
2005	8.58
2006	8.72
2007	8.86
2008	9
2009	9.14
2010	9.28
2011	9.42
2012	9.56
2013	9.7
2014	9.84
2015	9.98