Year	Years
1970	0.73
1971	0.75
1972	0.78
1973	0.8
1974	0.83
1975	0.86
1976	0.89
1977	0.92
1978	0.95
1979	0.99
1980	1.02
1981	1.06
1982	1.09
1983	1.13
1984	1.17
1985	1.21
1986	1.25
1987	1.3
1988	1.34
1989	1.39
1990	1.44
1991	1.49
1992	1.54
1993	1.59
1994	1.65
1995	1.7
1996	1.76
1997	1.82
1998	1.88
1999	1.94
2000	2
2001	2.06
2002	2.12
2003	2.19
2004	2.26
2005	2.33
2006	2.4
2007	2.47
2008	2.54
2009	2.62
2010	2.7
2011	2.77
2012	2.86
2013	2.94
2014	3.02
2015	3.11