Year	Years
1970	2.93
1971	3.01
1972	3.09
1973	3.17
1974	3.25
1975	3.33
1976	3.42
1977	3.51
1978	3.6
1979	3.7
1980	3.8
1981	3.9
1982	4
1983	4.11
1984	4.21
1985	4.33
1986	4.45
1987	4.57
1988	4.69
1989	4.82
1990	4.96
1991	5.1
1992	5.24
1993	5.4
1994	5.56
1995	5.73
1996	5.9
1997	6.07
1998	6.24
1999	6.4
2000	6.57
2001	6.73
2002	6.89
2003	7.05
2004	7.22
2005	7.37
2006	7.53
2007	7.69
2008	7.85
2009	8.01
2010	8.16
2011	8.32
2012	8.47
2013	8.63
2014	8.78
2015	8.93