Year	Years
1970	1.87
1971	1.94
1972	2
1973	2.07
1974	2.14
1975	2.21
1976	2.29
1977	2.37
1978	2.45
1979	2.54
1980	2.62
1981	2.71
1982	2.81
1983	2.91
1984	3.01
1985	3.12
1986	3.23
1987	3.35
1988	3.47
1989	3.6
1990	3.73
1991	3.88
1992	4.03
1993	4.18
1994	4.35
1995	4.53
1996	4.69
1997	4.85
1998	5.01
1999	5.18
2000	5.34
2001	5.5
2002	5.66
2003	5.83
2004	5.99
2005	6.16
2006	6.32
2007	6.49
2008	6.66
2009	6.83
2010	6.99
2011	7.16
2012	7.33
2013	7.5
2014	7.68
2015	7.85