Year	Years
1970	1.68
1971	1.74
1972	1.79
1973	1.85
1974	1.91
1975	1.97
1976	2.03
1977	2.09
1978	2.16
1979	2.22
1980	2.29
1981	2.36
1982	2.44
1983	2.51
1984	2.59
1985	2.67
1986	2.75
1987	2.83
1988	2.92
1989	3.01
1990	3.1
1991	3.19
1992	3.29
1993	3.38
1994	3.48
1995	3.59
1996	3.69
1997	3.8
1998	3.91
1999	4.02
2000	4.13
2001	4.25
2002	4.37
2003	4.49
2004	4.61
2005	4.74
2006	4.86
2007	4.99
2008	5.12
2009	5.26
2010	5.39
2011	5.53
2012	5.67
2013	5.81
2014	5.95
2015	6.1