Year	Years
1970	2.44
1971	2.5
1972	2.56
1973	2.63
1974	2.69
1975	2.76
1976	2.82
1977	2.89
1978	2.97
1979	3.04
1980	3.11
1981	3.19
1982	3.27
1983	3.35
1984	3.43
1985	3.52
1986	3.6
1987	3.69
1988	3.78
1989	3.88
1990	3.97
1991	4.07
1992	4.17
1993	4.28
1994	4.39
1995	4.5
1996	4.62
1997	4.74
1998	4.86
1999	4.99
2000	5.11
2001	5.24
2002	5.36
2003	5.49
2004	5.62
2005	5.75
2006	5.88
2007	6.01
2008	6.14
2009	6.27
2010	6.4
2011	6.53
2012	6.66
2013	6.8
2014	6.93
2015	7.06