Year	Years
1970	1.51
1971	1.55
1972	1.59
1973	1.63
1974	1.67
1975	1.72
1976	1.76
1977	1.81
1978	1.85
1979	1.9
1980	1.95
1981	2
1982	2.05
1983	2.1
1984	2.16
1985	2.21
1986	2.27
1987	2.32
1988	2.38
1989	2.44
1990	2.5
1991	2.56
1992	2.63
1993	2.69
1994	2.76
1995	2.82
1996	2.89
1997	2.95
1998	3.02
1999	3.09
2000	3.16
2001	3.23
2002	3.31
2003	3.38
2004	3.46
2005	3.54
2006	3.62
2007	3.7
2008	3.78
2009	3.86
2010	3.95
2011	4.03
2012	4.12
2013	4.21
2014	4.3
2015	4.4