Year	Years
1970	1.78
1971	1.85
1972	1.92
1973	2
1974	2.08
1975	2.16
1976	2.24
1977	2.33
1978	2.42
1979	2.51
1980	2.61
1981	2.71
1982	2.81
1983	2.92
1984	3.03
1985	3.15
1986	3.26
1987	3.39
1988	3.51
1989	3.64
1990	3.77
1991	3.91
1992	4.04
1993	4.18
1994	4.32
1995	4.47
1996	4.59
1997	4.71
1998	4.84
1999	4.96
2000	5.08
2001	5.21
2002	5.33
2003	5.46
2004	5.58
2005	5.71
2006	5.83
2007	5.96
2008	6.09
2009	6.22
2010	6.35
2011	6.48
2012	6.62
2013	6.75
2014	6.89
2015	7.02