Year	Years
1970	0.51
1971	0.52
1972	0.54
1973	0.55
1974	0.57
1975	0.59
1976	0.61
1977	0.63
1978	0.65
1979	0.67
1980	0.69
1981	0.71
1982	0.74
1983	0.76
1984	0.79
1985	0.81
1986	0.84
1987	0.87
1988	0.9
1989	0.94
1990	0.97
1991	1.01
1992	1.05
1993	1.09
1994	1.13
1995	1.18
1996	1.21
1997	1.25
1998	1.28
1999	1.32
2000	1.36
2001	1.39
2002	1.43
2003	1.47
2004	1.51
2005	1.55
2006	1.59
2007	1.64
2008	1.68
2009	1.73
2010	1.77
2011	1.82
2012	1.87
2013	1.92
2014	1.97
2015	2.02