Year	Years
1970	1.64
1971	1.69
1972	1.74
1973	1.8
1974	1.85
1975	1.91
1976	1.97
1977	2.03
1978	2.1
1979	2.16
1980	2.23
1981	2.3
1982	2.37
1983	2.44
1984	2.52
1985	2.59
1986	2.67
1987	2.75
1988	2.84
1989	2.92
1990	3.01
1991	3.1
1992	3.19
1993	3.29
1994	3.38
1995	3.48
1996	3.59
1997	3.7
1998	3.81
1999	3.92
2000	4.04
2001	4.15
2002	4.27
2003	4.39
2004	4.52
2005	4.64
2006	4.77
2007	4.9
2008	5.03
2009	5.16
2010	5.3
2011	5.43
2012	5.57
2013	5.71
2014	5.85
2015	6