Year	Years
1970	1.52
1971	1.58
1972	1.64
1973	1.71
1974	1.78
1975	1.85
1976	1.93
1977	2.01
1978	2.1
1979	2.19
1980	2.29
1981	2.39
1982	2.5
1983	2.62
1984	2.75
1985	2.88
1986	3.02
1987	3.18
1988	3.34
1989	3.51
1990	3.69
1991	3.87
1992	4.06
1993	4.26
1994	4.46
1995	4.66
1996	4.8
1997	4.93
1998	5.07
1999	5.2
2000	5.33
2001	5.47
2002	5.6
2003	5.74
2004	5.87
2005	6
2006	6.14
2007	6.27
2008	6.41
2009	6.54
2010	6.68
2011	6.81
2012	6.95
2013	7.08
2014	7.22
2015	7.36