Year	Years
1970	1.23
1971	1.27
1972	1.32
1973	1.37
1974	1.42
1975	1.47
1976	1.53
1977	1.58
1978	1.65
1979	1.71
1980	1.78
1981	1.85
1982	1.92
1983	2
1984	2.09
1985	2.17
1986	2.27
1987	2.37
1988	2.47
1989	2.58
1990	2.7
1991	2.82
1992	2.95
1993	3.08
1994	3.22
1995	3.37
1996	3.5
1997	3.62
1998	3.75
1999	3.88
2000	4
2001	4.13
2002	4.25
2003	4.38
2004	4.51
2005	4.64
2006	4.76
2007	4.89
2008	5.02
2009	5.15
2010	5.28
2011	5.41
2012	5.53
2013	5.66
2014	5.79
2015	5.92