Year	Years
1970	1.51
1971	1.56
1972	1.61
1973	1.66
1974	1.7
1975	1.75
1976	1.81
1977	1.86
1978	1.91
1979	1.96
1980	2.02
1981	2.07
1982	2.13
1983	2.19
1984	2.25
1985	2.31
1986	2.36
1987	2.42
1988	2.48
1989	2.54
1990	2.6
1991	2.66
1992	2.72
1993	2.78
1994	2.84
1995	2.89
1996	2.94
1997	2.99
1998	3.04
1999	3.1
2000	3.16
2001	3.22
2002	3.29
2003	3.36
2004	3.43
2005	3.5
2006	3.58
2007	3.66
2008	3.74
2009	3.82
2010	3.91
2011	4
2012	4.09
2013	4.18
2014	4.28
2015	4.38