Year	Years
1970	4.63
1971	4.73
1972	4.83
1973	4.93
1974	5.04
1975	5.15
1976	5.26
1977	5.37
1978	5.48
1979	5.6
1980	5.71
1981	5.83
1982	5.95
1983	6.07
1984	6.19
1985	6.31
1986	6.44
1987	6.57
1988	6.69
1989	6.82
1990	6.96
1991	7.09
1992	7.22
1993	7.36
1994	7.49
1995	7.63
1996	7.77
1997	7.9
1998	8.04
1999	8.17
2000	8.31
2001	8.44
2002	8.58
2003	8.72
2004	8.86
2005	8.99
2006	9.13
2007	9.27
2008	9.41
2009	9.55
2010	9.68
2011	9.82
2012	9.96
2013	10.1
2014	10.24
2015	10.38