Year	Years
1970	3.18
1971	3.25
1972	3.33
1973	3.4
1974	3.48
1975	3.56
1976	3.64
1977	3.73
1978	3.81
1979	3.9
1980	3.98
1981	4.07
1982	4.16
1983	4.25
1984	4.34
1985	4.43
1986	4.53
1987	4.62
1988	4.72
1989	4.81
1990	4.91
1991	5.01
1992	5.11
1993	5.21
1994	5.31
1995	5.42
1996	5.52
1997	5.62
1998	5.73
1999	5.83
2000	5.94
2001	6.05
2002	6.16
2003	6.28
2004	6.39
2005	6.51
2006	6.63
2007	6.75
2008	6.87
2009	6.99
2010	7.11
2011	7.24
2012	7.36
2013	7.49
2014	7.62
2015	7.75