Year	Years
1970	0.56
1971	0.58
1972	0.6
1973	0.62
1974	0.64
1975	0.66
1976	0.69
1977	0.71
1978	0.73
1979	0.76
1980	0.79
1981	0.81
1982	0.84
1983	0.87
1984	0.9
1985	0.94
1986	0.97
1987	1
1988	1.04
1989	1.08
1990	1.12
1991	1.16
1992	1.2
1993	1.24
1994	1.28
1995	1.33
1996	1.38
1997	1.43
1998	1.48
1999	1.53
2000	1.58
2001	1.64
2002	1.69
2003	1.75
2004	1.81
2005	1.86
2006	1.93
2007	1.99
2008	2.05
2009	2.11
2010	2.18
2011	2.25
2012	2.32
2013	2.39
2014	2.46
2015	2.54