Year	Years
1970	1.66
1971	1.72
1972	1.77
1973	1.83
1974	1.9
1975	1.96
1976	2.03
1977	2.1
1978	2.18
1979	2.25
1980	2.34
1981	2.42
1982	2.51
1983	2.61
1984	2.71
1985	2.82
1986	2.93
1987	3.05
1988	3.18
1989	3.32
1990	3.46
1991	3.62
1992	3.79
1993	3.97
1994	4.17
1995	4.38
1996	4.54
1997	4.71
1998	4.87
1999	5.03
2000	5.19
2001	5.35
2002	5.51
2003	5.66
2004	5.81
2005	5.97
2006	6.12
2007	6.27
2008	6.42
2009	6.56
2010	6.71
2011	6.86
2012	7.01
2013	7.15
2014	7.3
2015	7.44