Year	Years
1970	2.82
1971	2.88
1972	2.95
1973	3.01
1974	3.08
1975	3.15
1976	3.22
1977	3.3
1978	3.37
1979	3.44
1980	3.52
1981	3.59
1982	3.67
1983	3.75
1984	3.83
1985	3.91
1986	3.99
1987	4.07
1988	4.15
1989	4.23
1990	4.32
1991	4.4
1992	4.48
1993	4.57
1994	4.66
1995	4.75
1996	4.85
1997	4.95
1998	5.05
1999	5.16
2000	5.26
2001	5.37
2002	5.48
2003	5.59
2004	5.7
2005	5.82
2006	5.93
2007	6.05
2008	6.17
2009	6.29
2010	6.41
2011	6.53
2012	6.66
2013	6.78
2014	6.91
2015	7.04