Year	Years
1970	2.88
1971	2.95
1972	3.03
1973	3.11
1974	3.19
1975	3.28
1976	3.36
1977	3.45
1978	3.54
1979	3.64
1980	3.73
1981	3.83
1982	3.93
1983	4.03
1984	4.14
1985	4.25
1986	4.36
1987	4.47
1988	4.59
1989	4.71
1990	4.83
1991	4.95
1992	5.08
1993	5.2
1994	5.33
1995	5.45
1996	5.57
1997	5.68
1998	5.79
1999	5.91
2000	6.03
2001	6.14
2002	6.26
2003	6.38
2004	6.5
2005	6.63
2006	6.75
2007	6.87
2008	7
2009	7.13
2010	7.26
2011	7.39
2012	7.52
2013	7.65
2014	7.78
2015	7.91