Year	Years
1970	1.88
1971	1.94
1972	2
1973	2.07
1974	2.14
1975	2.21
1976	2.28
1977	2.35
1978	2.43
1979	2.51
1980	2.59
1981	2.68
1982	2.76
1983	2.85
1984	2.94
1985	3.04
1986	3.13
1987	3.23
1988	3.33
1989	3.44
1990	3.55
1991	3.66
1992	3.77
1993	3.88
1994	4
1995	4.12
1996	4.24
1997	4.36
1998	4.49
1999	4.61
2000	4.74
2001	4.87
2002	4.99
2003	5.12
2004	5.26
2005	5.39
2006	5.52
2007	5.66
2008	5.79
2009	5.93
2010	6.07
2011	6.2
2012	6.34
2013	6.48
2014	6.63
2015	6.77