Year	Years
1970	1.48
1971	1.52
1972	1.56
1973	1.6
1974	1.64
1975	1.68
1976	1.73
1977	1.77
1978	1.82
1979	1.87
1980	1.92
1981	1.97
1982	2.02
1983	2.07
1984	2.13
1985	2.18
1986	2.24
1987	2.3
1988	2.36
1989	2.42
1990	2.48
1991	2.54
1992	2.61
1993	2.68
1994	2.75
1995	2.82
1996	2.89
1997	2.97
1998	3.04
1999	3.12
2000	3.2
2001	3.28
2002	3.36
2003	3.44
2004	3.53
2005	3.61
2006	3.7
2007	3.79
2008	3.88
2009	3.97
2010	4.06
2011	4.15
2012	4.25
2013	4.34
2014	4.44
2015	4.54