Year	Years
1970	1.59
1971	1.63
1972	1.68
1973	1.72
1974	1.77
1975	1.82
1976	1.87
1977	1.92
1978	1.97
1979	2.02
1980	2.08
1981	2.13
1982	2.19
1983	2.25
1984	2.31
1985	2.37
1986	2.44
1987	2.5
1988	2.57
1989	2.64
1990	2.71
1991	2.78
1992	2.86
1993	2.93
1994	3.01
1995	3.1
1996	3.18
1997	3.27
1998	3.35
1999	3.44
2000	3.53
2001	3.62
2002	3.71
2003	3.8
2004	3.9
2005	3.99
2006	4.09
2007	4.18
2008	4.28
2009	4.38
2010	4.48
2011	4.58
2012	4.69
2013	4.79
2014	4.9
2015	5