Year	Years
1970	4.4
1971	4.5
1972	4.6
1973	4.7
1974	4.81
1975	4.91
1976	5.02
1977	5.13
1978	5.23
1979	5.34
1980	5.46
1981	5.57
1982	5.68
1983	5.79
1984	5.91
1985	6.02
1986	6.14
1987	6.26
1988	6.37
1989	6.49
1990	6.61
1991	6.73
1992	6.84
1993	6.96
1994	7.08
1995	7.2
1996	7.31
1997	7.42
1998	7.54
1999	7.66
2000	7.78
2001	7.89
2002	8.01
2003	8.13
2004	8.26
2005	8.38
2006	8.5
2007	8.63
2008	8.75
2009	8.88
2010	9
2011	9.13
2012	9.26
2013	9.39
2014	9.52
2015	9.65