Year	Years
1970	0.68
1971	0.7
1972	0.73
1973	0.75
1974	0.78
1975	0.81
1976	0.84
1977	0.87
1978	0.91
1979	0.94
1980	0.98
1981	1.01
1982	1.05
1983	1.09
1984	1.14
1985	1.18
1986	1.23
1987	1.28
1988	1.33
1989	1.39
1990	1.45
1991	1.51
1992	1.58
1993	1.65
1994	1.72
1995	1.8
1996	1.87
1997	1.94
1998	2.02
1999	2.09
2000	2.17
2001	2.24
2002	2.32
2003	2.4
2004	2.48
2005	2.57
2006	2.65
2007	2.74
2008	2.82
2009	2.91
2010	3.01
2011	3.1
2012	3.19
2013	3.29
2014	3.39
2015	3.49