Year	Years
1970	1.72
1971	1.76
1972	1.81
1973	1.85
1974	1.9
1975	1.95
1976	2
1977	2.06
1978	2.11
1979	2.16
1980	2.22
1981	2.28
1982	2.34
1983	2.39
1984	2.46
1985	2.52
1986	2.58
1987	2.65
1988	2.71
1989	2.78
1990	2.85
1991	2.92
1992	2.99
1993	3.07
1994	3.14
1995	3.22
1996	3.3
1997	3.38
1998	3.46
1999	3.54
2000	3.62
2001	3.71
2002	3.8
2003	3.88
2004	3.97
2005	4.06
2006	4.16
2007	4.25
2008	4.34
2009	4.44
2010	4.54
2011	4.64
2012	4.74
2013	4.84
2014	4.94
2015	5.05