Year	Years
1970	2.87
1971	2.94
1972	3.02
1973	3.09
1974	3.17
1975	3.26
1976	3.34
1977	3.42
1978	3.51
1979	3.6
1980	3.69
1981	3.78
1982	3.88
1983	3.98
1984	4.08
1985	4.18
1986	4.29
1987	4.39
1988	4.5
1989	4.61
1990	4.73
1991	4.84
1992	4.96
1993	5.08
1994	5.2
1995	5.32
1996	5.44
1997	5.55
1998	5.66
1999	5.78
2000	5.89
2001	6.01
2002	6.12
2003	6.24
2004	6.36
2005	6.48
2006	6.6
2007	6.72
2008	6.84
2009	6.96
2010	7.09
2011	7.21
2012	7.34
2013	7.47
2014	7.6
2015	7.73