Year	Years
1970	1.62
1971	1.68
1972	1.75
1973	1.82
1974	1.89
1975	1.96
1976	2.04
1977	2.12
1978	2.2
1979	2.29
1980	2.38
1981	2.48
1982	2.58
1983	2.68
1984	2.79
1985	2.91
1986	3.02
1987	3.15
1988	3.28
1989	3.42
1990	3.56
1991	3.71
1992	3.87
1993	4.03
1994	4.21
1995	4.39
1996	4.57
1997	4.75
1998	4.93
1999	5.11
2000	5.29
2001	5.47
2002	5.64
2003	5.82
2004	5.99
2005	6.17
2006	6.34
2007	6.51
2008	6.68
2009	6.84
2010	7.01
2011	7.18
2012	7.34
2013	7.5
2014	7.67
2015	7.83