Year	Years
1970	1
1971	1.04
1972	1.07
1973	1.11
1974	1.15
1975	1.18
1976	1.22
1977	1.27
1978	1.31
1979	1.35
1980	1.4
1981	1.45
1982	1.5
1983	1.55
1984	1.6
1985	1.66
1986	1.71
1987	1.77
1988	1.83
1989	1.89
1990	1.96
1991	2.02
1992	2.09
1993	2.16
1994	2.24
1995	2.31
1996	2.39
1997	2.48
1998	2.56
1999	2.64
2000	2.73
2001	2.82
2002	2.91
2003	3
2004	3.09
2005	3.18
2006	3.28
2007	3.38
2008	3.48
2009	3.58
2010	3.68
2011	3.79
2012	3.9
2013	4.01
2014	4.12
2015	4.23