Year	Years
1970	2.77
1971	2.85
1972	2.94
1973	3.03
1974	3.13
1975	3.22
1976	3.32
1977	3.42
1978	3.53
1979	3.63
1980	3.74
1981	3.86
1982	3.97
1983	4.09
1984	4.21
1985	4.33
1986	4.46
1987	4.59
1988	4.72
1989	4.85
1990	4.99
1991	5.13
1992	5.27
1993	5.42
1994	5.57
1995	5.72
1996	5.87
1997	6.03
1998	6.18
1999	6.34
2000	6.5
2001	6.66
2002	6.82
2003	6.98
2004	7.15
2005	7.31
2006	7.47
2007	7.64
2008	7.8
2009	7.97
2010	8.13
2011	8.3
2012	8.46
2013	8.63
2014	8.79
2015	8.96