Year	Years
1970	1.67
1971	1.72
1972	1.77
1973	1.82
1974	1.87
1975	1.92
1976	1.97
1977	2.02
1978	2.08
1979	2.13
1980	2.19
1981	2.25
1982	2.31
1983	2.37
1984	2.44
1985	2.5
1986	2.57
1987	2.64
1988	2.71
1989	2.78
1990	2.85
1991	2.92
1992	3
1993	3.07
1994	3.15
1995	3.23
1996	3.31
1997	3.38
1998	3.46
1999	3.54
2000	3.63
2001	3.71
2002	3.79
2003	3.88
2004	3.96
2005	4.05
2006	4.13
2007	4.22
2008	4.31
2009	4.4
2010	4.49
2011	4.58
2012	4.67
2013	4.76
2014	4.86
2015	4.95