Year	Years
1970	5.5
1971	5.6
1972	5.7
1973	5.8
1974	6
1975	6.1
1976	6.2
1977	6.3
1978	6.4
1979	6.5
1980	6.7
1981	6.8
1982	6.9
1983	7
1984	7.1
1985	7.2
1986	7.3
1987	7.4
1988	7.5
1989	7.5
1990	7.6
1991	7.7
1992	7.8
1993	7.9
1994	8
1995	8
1996	8.1
1997	8.2
1998	8.3
1999	8.3
2000	8.4
2001	8.5
2002	8.6
2003	8.6
2004	8.7
2005	8.8
2006	8.8
2007	8.9
2008	9
2009	9