Year	Years
1970	2.8
1971	2.88
1972	2.97
1973	3.05
1974	3.14
1975	3.23
1976	3.32
1977	3.42
1978	3.52
1979	3.61
1980	3.72
1981	3.82
1982	3.92
1983	4.03
1984	4.14
1985	4.26
1986	4.37
1987	4.49
1988	4.61
1989	4.73
1990	4.85
1991	4.98
1992	5.11
1993	5.24
1994	5.37
1995	5.51
1996	5.66
1997	5.8
1998	5.95
1999	6.1
2000	6.25
2001	6.4
2002	6.56
2003	6.72
2004	6.87
2005	7.03
2006	7.19
2007	7.36
2008	7.52
2009	7.68
2010	7.85
2011	8.02
2012	8.18
2013	8.35
2014	8.52
2015	8.69