Year	Years
1970	2.9
1971	2.97
1972	3.04
1973	3.12
1974	3.19
1975	3.27
1976	3.35
1977	3.43
1978	3.52
1979	3.6
1980	3.69
1981	3.78
1982	3.87
1983	3.96
1984	4.05
1985	4.15
1986	4.24
1987	4.34
1988	4.44
1989	4.54
1990	4.65
1991	4.75
1992	4.86
1993	4.97
1994	5.08
1995	5.19
1996	5.3
1997	5.42
1998	5.53
1999	5.65
2000	5.77
2001	5.88
2002	6
2003	6.12
2004	6.25
2005	6.37
2006	6.49
2007	6.62
2008	6.74
2009	6.87
2010	6.99
2011	7.12
2012	7.25
2013	7.38
2014	7.51
2015	7.64