Year	Years
1970	1.78
1971	1.84
1972	1.89
1973	1.95
1974	2.01
1975	2.07
1976	2.13
1977	2.2
1978	2.26
1979	2.32
1980	2.39
1981	2.46
1982	2.52
1983	2.59
1984	2.66
1985	2.73
1986	2.8
1987	2.88
1988	2.95
1989	3.02
1990	3.1
1991	3.17
1992	3.24
1993	3.32
1994	3.39
1995	3.47
1996	3.55
1997	3.63
1998	3.71
1999	3.79
2000	3.88
2001	3.97
2002	4.06
2003	4.16
2004	4.26
2005	4.36
2006	4.46
2007	4.57
2008	4.67
2009	4.79
2010	4.9
2011	5.02
2012	5.14
2013	5.26
2014	5.38
2015	5.51