Year	Years
1970	2.69
1971	2.75
1972	2.82
1973	2.89
1974	2.97
1975	3.04
1976	3.12
1977	3.19
1978	3.27
1979	3.35
1980	3.44
1981	3.52
1982	3.61
1983	3.7
1984	3.79
1985	3.88
1986	3.97
1987	4.07
1988	4.17
1989	4.27
1990	4.37
1991	4.48
1992	4.58
1993	4.7
1994	4.81
1995	4.92
1996	5.04
1997	5.15
1998	5.27
1999	5.39
2000	5.5
2001	5.62
2002	5.74
2003	5.87
2004	5.99
2005	6.11
2006	6.24
2007	6.36
2008	6.49
2009	6.62
2010	6.75
2011	6.88
2012	7.01
2013	7.14
2014	7.27
2015	7.4