Year	Years
1970	2.99
1971	3.06
1972	3.14
1973	3.21
1974	3.29
1975	3.37
1976	3.46
1977	3.54
1978	3.62
1979	3.71
1980	3.8
1981	3.89
1982	3.98
1983	4.07
1984	4.17
1985	4.26
1986	4.36
1987	4.46
1988	4.56
1989	4.66
1990	4.77
1991	4.87
1992	4.98
1993	5.09
1994	5.2
1995	5.31
1996	5.42
1997	5.53
1998	5.64
1999	5.75
2000	5.86
2001	5.98
2002	6.09
2003	6.21
2004	6.32
2005	6.44
2006	6.56
2007	6.68
2008	6.8
2009	6.92
2010	7.05
2011	7.17
2012	7.3
2013	7.42
2014	7.55
2015	7.68