Year	Years
1970	1.76
1971	1.81
1972	1.87
1973	1.92
1974	1.98
1975	2.04
1976	2.1
1977	2.16
1978	2.22
1979	2.29
1980	2.36
1981	2.43
1982	2.5
1983	2.58
1984	2.66
1985	2.74
1986	2.82
1987	2.91
1988	2.99
1989	3.08
1990	3.18
1991	3.27
1992	3.37
1993	3.47
1994	3.57
1995	3.68
1996	3.78
1997	3.88
1998	3.99
1999	4.1
2000	4.21
2001	4.31
2002	4.43
2003	4.54
2004	4.65
2005	4.77
2006	4.88
2007	5
2008	5.12
2009	5.24
2010	5.36
2011	5.48
2012	5.6
2013	5.72
2014	5.84
2015	5.97