Year	Years
1970	1.47
1971	1.51
1972	1.56
1973	1.6
1974	1.65
1975	1.69
1976	1.74
1977	1.79
1978	1.84
1979	1.9
1980	1.95
1981	2.01
1982	2.07
1983	2.13
1984	2.19
1985	2.25
1986	2.32
1987	2.39
1988	2.46
1989	2.53
1990	2.61
1991	2.68
1992	2.76
1993	2.84
1994	2.93
1995	3.01
1996	3.1
1997	3.19
1998	3.29
1999	3.38
2000	3.48
2001	3.57
2002	3.67
2003	3.76
2004	3.86
2005	3.96
2006	4.06
2007	4.16
2008	4.26
2009	4.36
2010	4.46
2011	4.56
2012	4.67
2013	4.77
2014	4.87
2015	4.97