Year	Years
1970	1.54
1971	1.57
1972	1.6
1973	1.63
1974	1.67
1975	1.7
1976	1.73
1977	1.76
1978	1.79
1979	1.82
1980	1.85
1981	1.88
1982	1.92
1983	1.95
1984	1.98
1985	2.01
1986	2.05
1987	2.08
1988	2.12
1989	2.16
1990	2.2
1991	2.24
1992	2.28
1993	2.32
1994	2.37
1995	2.42
1996	2.49
1997	2.56
1998	2.63
1999	2.7
2000	2.78
2001	2.86
2002	2.95
2003	3.03
2004	3.12
2005	3.21
2006	3.3
2007	3.39
2008	3.49
2009	3.58
2010	3.68
2011	3.78
2012	3.89
2013	3.99
2014	4.09
2015	4.2