Year	Years
1970	1.47
1971	1.51
1972	1.55
1973	1.59
1974	1.63
1975	1.67
1976	1.71
1977	1.76
1978	1.8
1979	1.85
1980	1.9
1981	1.95
1982	2
1983	2.05
1984	2.1
1985	2.15
1986	2.21
1987	2.27
1988	2.32
1989	2.38
1990	2.44
1991	2.5
1992	2.56
1993	2.63
1994	2.69
1995	2.76
1996	2.83
1997	2.89
1998	2.96
1999	3.04
2000	3.11
2001	3.18
2002	3.26
2003	3.33
2004	3.41
2005	3.49
2006	3.57
2007	3.66
2008	3.74
2009	3.83
2010	3.91
2011	4
2012	4.09
2013	4.19
2014	4.28
2015	4.37