Year	Years
1970	3.88
1971	3.97
1972	4.06
1973	4.16
1974	4.25
1975	4.35
1976	4.45
1977	4.55
1978	4.65
1979	4.76
1980	4.86
1981	4.97
1982	5.08
1983	5.19
1984	5.31
1985	5.42
1986	5.53
1987	5.65
1988	5.77
1989	5.89
1990	6.01
1991	6.13
1992	6.26
1993	6.38
1994	6.51
1995	6.64
1996	6.76
1997	6.89
1998	7.02
1999	7.15
2000	7.29
2001	7.42
2002	7.55
2003	7.68
2004	7.82
2005	7.95
2006	8.09
2007	8.22
2008	8.36
2009	8.49
2010	8.63
2011	8.76
2012	8.9
2013	9.03
2014	9.17
2015	9.3