Year	Years
1970	0.97
1971	1
1972	1.04
1973	1.08
1974	1.11
1975	1.15
1976	1.19
1977	1.24
1978	1.28
1979	1.33
1980	1.37
1981	1.42
1982	1.48
1983	1.53
1984	1.58
1985	1.64
1986	1.7
1987	1.76
1988	1.83
1989	1.9
1990	1.97
1991	2.04
1992	2.11
1993	2.19
1994	2.27
1995	2.36
1996	2.45
1997	2.54
1998	2.63
1999	2.73
2000	2.82
2001	2.92
2002	3.02
2003	3.12
2004	3.23
2005	3.33
2006	3.44
2007	3.55
2008	3.66
2009	3.77
2010	3.89
2011	4
2012	4.12
2013	4.24
2014	4.36
2015	4.48