Year	Years
1970	0.42
1971	0.43
1972	0.45
1973	0.47
1974	0.48
1975	0.5
1976	0.52
1977	0.54
1978	0.56
1979	0.58
1980	0.6
1981	0.62
1982	0.65
1983	0.67
1984	0.69
1985	0.72
1986	0.75
1987	0.77
1988	0.8
1989	0.83
1990	0.86
1991	0.9
1992	0.93
1993	0.96
1994	1
1995	1.04
1996	1.07
1997	1.11
1998	1.15
1999	1.19
2000	1.23
2001	1.27
2002	1.32
2003	1.36
2004	1.41
2005	1.45
2006	1.5
2007	1.55
2008	1.6
2009	1.65
2010	1.7
2011	1.75
2012	1.81
2013	1.86
2014	1.92
2015	1.97