Year	Years
1970	2.89
1971	2.96
1972	3.03
1973	3.11
1974	3.18
1975	3.25
1976	3.33
1977	3.41
1978	3.49
1979	3.57
1980	3.65
1981	3.73
1982	3.82
1983	3.9
1984	3.99
1985	4.08
1986	4.17
1987	4.26
1988	4.36
1989	4.45
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	5.38
1999	5.49
2000	5.61
2001	5.72
2002	5.84
2003	5.95
2004	6.07
2005	6.19
2006	6.32
2007	6.44
2008	6.56
2009	6.69
2010	6.82
2011	6.94
2012	7.07
2013	7.2
2014	7.33
2015	7.47