Year	Years
1970	1.58
1971	1.62
1972	1.66
1973	1.71
1974	1.75
1975	1.8
1976	1.85
1977	1.9
1978	1.95
1979	2
1980	2.05
1981	2.1
1982	2.16
1983	2.22
1984	2.27
1985	2.33
1986	2.39
1987	2.45
1988	2.52
1989	2.58
1990	2.65
1991	2.72
1992	2.79
1993	2.86
1994	2.93
1995	3
1996	3.08
1997	3.15
1998	3.23
1999	3.31
2000	3.4
2001	3.48
2002	3.56
2003	3.65
2004	3.74
2005	3.83
2006	3.92
2007	4.01
2008	4.1
2009	4.2
2010	4.29
2011	4.39
2012	4.49
2013	4.59
2014	4.69
2015	4.79