Year	Years
1970	1.68
1971	1.74
1972	1.79
1973	1.85
1974	1.91
1975	1.97
1976	2.03
1977	2.1
1978	2.16
1979	2.23
1980	2.3
1981	2.38
1982	2.45
1983	2.53
1984	2.61
1985	2.69
1986	2.77
1987	2.86
1988	2.95
1989	3.04
1990	3.14
1991	3.23
1992	3.33
1993	3.44
1994	3.54
1995	3.65
1996	3.78
1997	3.91
1998	4.03
1999	4.16
2000	4.3
2001	4.43
2002	4.56
2003	4.7
2004	4.84
2005	4.98
2006	5.12
2007	5.26
2008	5.41
2009	5.55
2010	5.7
2011	5.85
2012	6
2013	6.15
2014	6.3
2015	6.45