Year	Years
1970	1.31
1971	1.35
1972	1.4
1973	1.45
1974	1.5
1975	1.56
1976	1.62
1977	1.68
1978	1.74
1979	1.81
1980	1.87
1981	1.94
1982	2.02
1983	2.1
1984	2.18
1985	2.27
1986	2.36
1987	2.45
1988	2.56
1989	2.66
1990	2.78
1991	2.9
1992	3.03
1993	3.17
1994	3.32
1995	3.48
1996	3.62
1997	3.77
1998	3.91
1999	4.06
2000	4.2
2001	4.35
2002	4.5
2003	4.64
2004	4.79
2005	4.94
2006	5.09
2007	5.25
2008	5.4
2009	5.55
2010	5.71
2011	5.86
2012	6.02
2013	6.18
2014	6.34
2015	6.5