Year	Years
1970	1.62
1971	1.67
1972	1.73
1973	1.78
1974	1.84
1975	1.9
1976	1.96
1977	2.03
1978	2.09
1979	2.16
1980	2.24
1981	2.31
1982	2.39
1983	2.47
1984	2.56
1985	2.64
1986	2.74
1987	2.83
1988	2.93
1989	3.03
1990	3.14
1991	3.24
1992	3.36
1993	3.47
1994	3.59
1995	3.71
1996	3.8
1997	3.9
1998	4
1999	4.1
2000	4.2
2001	4.3
2002	4.41
2003	4.51
2004	4.62
2005	4.72
2006	4.83
2007	4.94
2008	5.05
2009	5.16
2010	5.27
2011	5.38
2012	5.5
2013	5.61
2014	5.73
2015	5.85