Year	Years
1970	2.71
1971	2.79
1972	2.87
1973	2.95
1974	3.04
1975	3.13
1976	3.22
1977	3.32
1978	3.42
1979	3.52
1980	3.62
1981	3.73
1982	3.84
1983	3.95
1984	4.07
1985	4.19
1986	4.32
1987	4.44
1988	4.58
1989	4.71
1990	4.85
1991	5
1992	5.15
1993	5.31
1994	5.47
1995	5.64
1996	5.8
1997	5.96
1998	6.12
1999	6.27
2000	6.43
2001	6.59
2002	6.74
2003	6.89
2004	7.05
2005	7.2
2006	7.35
2007	7.49
2008	7.64
2009	7.79
2010	7.93
2011	8.08
2012	8.22
2013	8.36
2014	8.51
2015	8.65