Year	Years
1970	0.57
1971	0.58
1972	0.6
1973	0.62
1974	0.63
1975	0.65
1976	0.67
1977	0.69
1978	0.71
1979	0.73
1980	0.75
1981	0.77
1982	0.79
1983	0.82
1984	0.84
1985	0.87
1986	0.89
1987	0.92
1988	0.94
1989	0.97
1990	1
1991	1.03
1992	1.06
1993	1.09
1994	1.12
1995	1.16
1996	1.19
1997	1.23
1998	1.27
1999	1.3
2000	1.34
2001	1.38
2002	1.42
2003	1.46
2004	1.5
2005	1.55
2006	1.59
2007	1.63
2008	1.68
2009	1.72
2010	1.77
2011	1.82
2012	1.87
2013	1.92
2014	1.97
2015	2.02