Year	Years
1970	0.5
1971	0.51
1972	0.53
1973	0.55
1974	0.57
1975	0.59
1976	0.61
1977	0.63
1978	0.65
1979	0.67
1980	0.7
1981	0.72
1982	0.75
1983	0.77
1984	0.8
1985	0.83
1986	0.86
1987	0.89
1988	0.92
1989	0.95
1990	0.98
1991	1.02
1992	1.05
1993	1.09
1994	1.13
1995	1.17
1996	1.21
1997	1.26
1998	1.3
1999	1.35
2000	1.4
2001	1.44
2002	1.5
2003	1.55
2004	1.6
2005	1.66
2006	1.71
2007	1.77
2008	1.83
2009	1.89
2010	1.95
2011	2.02
2012	2.08
2013	2.15
2014	2.22
2015	2.29