Year	Years
1970	1.88
1971	1.94
1972	2
1973	2.07
1974	2.13
1975	2.2
1976	2.27
1977	2.35
1978	2.42
1979	2.5
1980	2.58
1981	2.66
1982	2.74
1983	2.82
1984	2.91
1985	3
1986	3.09
1987	3.18
1988	3.28
1989	3.38
1990	3.47
1991	3.57
1992	3.68
1993	3.78
1994	3.88
1995	3.99
1996	4.09
1997	4.2
1998	4.31
1999	4.42
2000	4.53
2001	4.64
2002	4.75
2003	4.87
2004	4.98
2005	5.1
2006	5.22
2007	5.35
2008	5.47
2009	5.6
2010	5.73
2011	5.86
2012	5.99
2013	6.12
2014	6.26
2015	6.4