Year	Years
1970	4.7
1971	4.83
1972	4.95
1973	5.08
1974	5.21
1975	5.34
1976	5.47
1977	5.61
1978	5.74
1979	5.88
1980	6.03
1981	6.17
1982	6.31
1983	6.46
1984	6.61
1985	6.76
1986	6.91
1987	7.06
1988	7.22
1989	7.37
1990	7.53
1991	7.69
1992	7.85
1993	8.01
1994	8.17
1995	8.34
1996	8.5
1997	8.66
1998	8.83
1999	9
2000	9.16
2001	9.33
2002	9.5
2003	9.66
2004	9.83
2005	10
2006	10.17
2007	10.34
2008	10.5
2009	10.67
2010	10.84
2011	11
2012	11.17
2013	11.34
2014	11.5
2015	11.66