Year	Years
1970	2.21
1971	2.28
1972	2.35
1973	2.42
1974	2.5
1975	2.58
1976	2.66
1977	2.74
1978	2.82
1979	2.91
1980	3
1981	3.09
1982	3.18
1983	3.27
1984	3.37
1985	3.46
1986	3.56
1987	3.66
1988	3.77
1989	3.87
1990	3.97
1991	4.08
1992	4.19
1993	4.3
1994	4.41
1995	4.52
1996	4.63
1997	4.74
1998	4.86
1999	4.97
2000	5.09
2001	5.21
2002	5.33
2003	5.45
2004	5.58
2005	5.7
2006	5.83
2007	5.96
2008	6.09
2009	6.22
2010	6.36
2011	6.49
2012	6.63
2013	6.77
2014	6.91
2015	7.05