Year	Years
1970	4.51
1971	4.61
1972	4.71
1973	4.81
1974	4.92
1975	5.02
1976	5.13
1977	5.23
1978	5.34
1979	5.45
1980	5.56
1981	5.67
1982	5.79
1983	5.9
1984	6.02
1985	6.13
1986	6.25
1987	6.37
1988	6.49
1989	6.61
1990	6.73
1991	6.85
1992	6.97
1993	7.09
1994	7.22
1995	7.34
1996	7.46
1997	7.59
1998	7.72
1999	7.84
2000	7.97
2001	8.1
2002	8.23
2003	8.37
2004	8.5
2005	8.63
2006	8.76
2007	8.9
2008	9.03
2009	9.17
2010	9.31
2011	9.44
2012	9.58
2013	9.72
2014	9.85
2015	9.99