Year	Years
1970	0.39
1971	0.41
1972	0.42
1973	0.43
1974	0.45
1975	0.47
1976	0.48
1977	0.5
1978	0.52
1979	0.53
1980	0.55
1981	0.57
1982	0.59
1983	0.61
1984	0.63
1985	0.66
1986	0.68
1987	0.7
1988	0.73
1989	0.75
1990	0.78
1991	0.81
1992	0.83
1993	0.86
1994	0.89
1995	0.93
1996	0.96
1997	0.99
1998	1.03
1999	1.06
2000	1.1
2001	1.14
2002	1.17
2003	1.21
2004	1.25
2005	1.3
2006	1.34
2007	1.38
2008	1.43
2009	1.47
2010	1.52
2011	1.57
2012	1.62
2013	1.67
2014	1.72
2015	1.77