Year	Years
1970	1.59
1971	1.64
1972	1.69
1973	1.75
1974	1.81
1975	1.86
1976	1.92
1977	1.99
1978	2.05
1979	2.12
1980	2.19
1981	2.26
1982	2.33
1983	2.41
1984	2.49
1985	2.57
1986	2.65
1987	2.74
1988	2.83
1989	2.92
1990	3.01
1991	3.11
1992	3.21
1993	3.32
1994	3.42
1995	3.54
1996	3.66
1997	3.78
1998	3.9
1999	4.02
2000	4.14
2001	4.27
2002	4.4
2003	4.53
2004	4.66
2005	4.79
2006	4.92
2007	5.06
2008	5.2
2009	5.34
2010	5.48
2011	5.63
2012	5.77
2013	5.92
2014	6.07
2015	6.22