Year	Years
1970	1.42
1971	1.46
1972	1.51
1973	1.55
1974	1.6
1975	1.65
1976	1.7
1977	1.75
1978	1.8
1979	1.86
1980	1.91
1981	1.97
1982	2.03
1983	2.09
1984	2.15
1985	2.21
1986	2.28
1987	2.34
1988	2.41
1989	2.48
1990	2.55
1991	2.62
1992	2.69
1993	2.77
1994	2.84
1995	2.92
1996	3
1997	3.08
1998	3.16
1999	3.25
2000	3.34
2001	3.43
2002	3.52
2003	3.61
2004	3.71
2005	3.81
2006	3.91
2007	4.02
2008	4.12
2009	4.23
2010	4.35
2011	4.46
2012	4.58
2013	4.7
2014	4.82
2015	4.94