Year	Years
1970	0.63
1971	0.66
1972	0.69
1973	0.72
1974	0.76
1975	0.8
1976	0.84
1977	0.88
1978	0.92
1979	0.97
1980	1.02
1981	1.08
1982	1.14
1983	1.2
1984	1.27
1985	1.34
1986	1.42
1987	1.5
1988	1.59
1989	1.68
1990	1.78
1991	1.89
1992	2
1993	2.12
1994	2.25
1995	2.38
1996	2.49
1997	2.6
1998	2.7
1999	2.81
2000	2.92
2001	3.03
2002	3.14
2003	3.25
2004	3.36
2005	3.48
2006	3.59
2007	3.71
2008	3.83
2009	3.94
2010	4.06
2011	4.19
2012	4.31
2013	4.43
2014	4.56
2015	4.68