Year	Years
1970	1.81
1971	1.85
1972	1.9
1973	1.95
1974	2
1975	2.05
1976	2.1
1977	2.15
1978	2.2
1979	2.26
1980	2.31
1981	2.37
1982	2.43
1983	2.48
1984	2.54
1985	2.6
1986	2.67
1987	2.73
1988	2.79
1989	2.86
1990	2.92
1991	2.99
1992	3.06
1993	3.13
1994	3.2
1995	3.27
1996	3.34
1997	3.42
1998	3.5
1999	3.58
2000	3.66
2001	3.74
2002	3.82
2003	3.91
2004	4
2005	4.09
2006	4.18
2007	4.27
2008	4.37
2009	4.46
2010	4.56
2011	4.66
2012	4.76
2013	4.86
2014	4.96
2015	5.07