Year	Years
1970	0.52
1971	0.55
1972	0.57
1973	0.6
1974	0.62
1975	0.65
1976	0.68
1977	0.72
1978	0.75
1979	0.79
1980	0.83
1981	0.87
1982	0.91
1983	0.96
1984	1.01
1985	1.07
1986	1.12
1987	1.19
1988	1.25
1989	1.32
1990	1.39
1991	1.47
1992	1.55
1993	1.64
1994	1.73
1995	1.82
1996	1.89
1997	1.96
1998	2.03
1999	2.11
2000	2.18
2001	2.25
2002	2.33
2003	2.4
2004	2.48
2005	2.56
2006	2.64
2007	2.71
2008	2.79
2009	2.88
2010	2.96
2011	3.04
2012	3.12
2013	3.21
2014	3.29
2015	3.38