Year	Years
1970	1.74
1971	1.8
1972	1.86
1973	1.93
1974	2
1975	2.07
1976	2.14
1977	2.22
1978	2.3
1979	2.38
1980	2.46
1981	2.55
1982	2.64
1983	2.73
1984	2.83
1985	2.93
1986	3.03
1987	3.14
1988	3.25
1989	3.36
1990	3.48
1991	3.6
1992	3.72
1993	3.85
1994	3.98
1995	4.11
1996	4.23
1997	4.35
1998	4.47
1999	4.59
2000	4.72
2001	4.85
2002	4.98
2003	5.11
2004	5.24
2005	5.37
2006	5.51
2007	5.65
2008	5.79
2009	5.93
2010	6.08
2011	6.22
2012	6.37
2013	6.52
2014	6.67
2015	6.82