Year	Years
1970	3.09
1971	3.18
1972	3.28
1973	3.37
1974	3.47
1975	3.58
1976	3.68
1977	3.79
1978	3.9
1979	4.01
1980	4.13
1981	4.25
1982	4.37
1983	4.49
1984	4.62
1985	4.76
1986	4.89
1987	5.03
1988	5.17
1989	5.32
1990	5.47
1991	5.62
1992	5.78
1993	5.95
1994	6.11
1995	6.29
1996	6.46
1997	6.63
1998	6.81
1999	6.99
2000	7.16
2001	7.34
2002	7.52
2003	7.7
2004	7.88
2005	8.06
2006	8.24
2007	8.42
2008	8.61
2009	8.79
2010	8.97
2011	9.15
2012	9.33
2013	9.51
2014	9.69
2015	9.87