Year	Years
1970	1.73
1971	1.78
1972	1.84
1973	1.9
1974	1.97
1975	2.03
1976	2.1
1977	2.17
1978	2.24
1979	2.31
1980	2.38
1981	2.46
1982	2.54
1983	2.62
1984	2.71
1985	2.79
1986	2.88
1987	2.97
1988	3.06
1989	3.16
1990	3.26
1991	3.36
1992	3.46
1993	3.57
1994	3.68
1995	3.79
1996	3.9
1997	4.02
1998	4.14
1999	4.25
2000	4.37
2001	4.5
2002	4.62
2003	4.74
2004	4.87
2005	4.99
2006	5.12
2007	5.25
2008	5.38
2009	5.52
2010	5.65
2011	5.79
2012	5.92
2013	6.06
2014	6.2
2015	6.35