Year	Years
1970	1.37
1971	1.41
1972	1.46
1973	1.5
1974	1.55
1975	1.6
1976	1.65
1977	1.7
1978	1.75
1979	1.8
1980	1.86
1981	1.91
1982	1.97
1983	2.03
1984	2.09
1985	2.15
1986	2.21
1987	2.27
1988	2.34
1989	2.4
1990	2.47
1991	2.54
1992	2.61
1993	2.68
1994	2.76
1995	2.83
1996	2.91
1997	3
1998	3.08
1999	3.17
2000	3.25
2001	3.35
2002	3.44
2003	3.53
2004	3.63
2005	3.73
2006	3.83
2007	3.94
2008	4.05
2009	4.16
2010	4.27
2011	4.38
2012	4.5
2013	4.61
2014	4.73
2015	4.86