Year	Years
1970	0.82
1971	0.85
1972	0.88
1973	0.92
1974	0.96
1975	1
1976	1.04
1977	1.09
1978	1.13
1979	1.18
1980	1.23
1981	1.29
1982	1.34
1983	1.4
1984	1.47
1985	1.53
1986	1.6
1987	1.67
1988	1.75
1989	1.83
1990	1.91
1991	2
1992	2.09
1993	2.18
1994	2.27
1995	2.37
1996	2.46
1997	2.56
1998	2.65
1999	2.75
2000	2.85
2001	2.95
2002	3.06
2003	3.16
2004	3.27
2005	3.38
2006	3.49
2007	3.61
2008	3.72
2009	3.84
2010	3.96
2011	4.08
2012	4.2
2013	4.32
2014	4.45
2015	4.57