Year	Years
1970	1.91
1971	1.97
1972	2.03
1973	2.09
1974	2.16
1975	2.23
1976	2.29
1977	2.36
1978	2.44
1979	2.51
1980	2.59
1981	2.67
1982	2.75
1983	2.83
1984	2.91
1985	3
1986	3.09
1987	3.18
1988	3.27
1989	3.36
1990	3.46
1991	3.55
1992	3.65
1993	3.75
1994	3.86
1995	3.96
1996	4.07
1997	4.17
1998	4.28
1999	4.4
2000	4.51
2001	4.63
2002	4.74
2003	4.86
2004	4.99
2005	5.11
2006	5.24
2007	5.36
2008	5.5
2009	5.63
2010	5.76
2011	5.9
2012	6.04
2013	6.18
2014	6.32
2015	6.46