Year	Years
1970	0.53
1971	0.55
1972	0.57
1973	0.59
1974	0.61
1975	0.63
1976	0.65
1977	0.67
1978	0.7
1979	0.72
1980	0.75
1981	0.77
1982	0.8
1983	0.83
1984	0.86
1985	0.88
1986	0.92
1987	0.95
1988	0.98
1989	1.01
1990	1.05
1991	1.08
1992	1.12
1993	1.16
1994	1.2
1995	1.24
1996	1.29
1997	1.33
1998	1.38
1999	1.43
2000	1.48
2001	1.53
2002	1.58
2003	1.63
2004	1.68
2005	1.74
2006	1.8
2007	1.86
2008	1.92
2009	1.98
2010	2.04
2011	2.1
2012	2.17
2013	2.24
2014	2.3
2015	2.38