Year	Years
1970	0.22
1971	0.23
1972	0.24
1973	0.25
1974	0.26
1975	0.28
1976	0.29
1977	0.31
1978	0.32
1979	0.34
1980	0.36
1981	0.38
1982	0.4
1983	0.43
1984	0.45
1985	0.48
1986	0.51
1987	0.54
1988	0.57
1989	0.61
1990	0.65
1991	0.69
1992	0.73
1993	0.78
1994	0.84
1995	0.9
1996	0.96
1997	1.02
1998	1.09
1999	1.15
2000	1.22
2001	1.29
2002	1.36
2003	1.44
2004	1.51
2005	1.58
2006	1.66
2007	1.73
2008	1.81
2009	1.88
2010	1.96
2011	2.03
2012	2.1
2013	2.17
2014	2.25
2015	2.31