Year	Years
1970	3.82
1971	3.92
1972	4.03
1973	4.14
1974	4.25
1975	4.36
1976	4.48
1977	4.6
1978	4.72
1979	4.84
1980	4.97
1981	5.09
1982	5.22
1983	5.35
1984	5.49
1985	5.62
1986	5.76
1987	5.9
1988	6.04
1989	6.18
1990	6.33
1991	6.47
1992	6.62
1993	6.77
1994	6.92
1995	7.08
1996	7.23
1997	7.39
1998	7.54
1999	7.7
2000	7.86
2001	8.02
2002	8.19
2003	8.35
2004	8.51
2005	8.68
2006	8.84
2007	9.01
2008	9.18
2009	9.34
2010	9.51
2011	9.68
2012	9.85
2013	10.02
2014	10.19
2015	10.35