Year	Years
1970	2.65
1971	2.74
1972	2.82
1973	2.9
1974	2.99
1975	3.08
1976	3.18
1977	3.27
1978	3.37
1979	3.47
1980	3.57
1981	3.68
1982	3.78
1983	3.89
1984	4.01
1985	4.12
1986	4.24
1987	4.36
1988	4.48
1989	4.61
1990	4.74
1991	4.87
1992	5
1993	5.14
1994	5.28
1995	5.42
1996	5.56
1997	5.7
1998	5.84
1999	5.98
2000	6.13
2001	6.27
2002	6.42
2003	6.57
2004	6.72
2005	6.87
2006	7.02
2007	7.17
2008	7.33
2009	7.48
2010	7.64
2011	7.8
2012	7.95
2013	8.11
2014	8.28
2015	8.44