Year	Years
1970	2.92
1971	2.99
1972	3.06
1973	3.13
1974	3.21
1975	3.28
1976	3.35
1977	3.43
1978	3.51
1979	3.59
1980	3.67
1981	3.75
1982	3.83
1983	3.92
1984	4
1985	4.09
1986	4.18
1987	4.27
1988	4.36
1989	4.46
1990	4.55
1991	4.65
1992	4.75
1993	4.85
1994	4.95
1995	5.06
1996	5.16
1997	5.27
1998	5.39
1999	5.5
2000	5.61
2001	5.73
2002	5.85
2003	5.97
2004	6.09
2005	6.21
2006	6.34
2007	6.46
2008	6.59
2009	6.72
2010	6.85
2011	6.98
2012	7.12
2013	7.25
2014	7.39
2015	7.52