Year	Years
1970	2.64
1971	2.71
1972	2.78
1973	2.85
1974	2.92
1975	2.99
1976	3.06
1977	3.14
1978	3.22
1979	3.3
1980	3.38
1981	3.46
1982	3.55
1983	3.64
1984	3.73
1985	3.82
1986	3.91
1987	4
1988	4.1
1989	4.2
1990	4.3
1991	4.4
1992	4.51
1993	4.61
1994	4.72
1995	4.83
1996	4.94
1997	5.05
1998	5.16
1999	5.27
2000	5.38
2001	5.49
2002	5.61
2003	5.72
2004	5.84
2005	5.96
2006	6.08
2007	6.2
2008	6.32
2009	6.44
2010	6.57
2011	6.69
2012	6.82
2013	6.95
2014	7.08
2015	7.21