Year	Years
1970	8.1
1971	8.2
1972	8.4
1973	8.5
1974	8.7
1975	8.8
1976	8.9
1977	9.1
1978	9.2
1979	9.3
1980	9.5
1981	9.6
1982	9.7
1983	9.8
1984	10
1985	10.1
1986	10.2
1987	10.3
1988	10.4
1989	10.5
1990	10.6
1991	10.7
1992	10.8
1993	11
1994	11.1
1995	11.1
1996	11.2
1997	11.3
1998	11.4
1999	11.5
2000	11.6
2001	11.7
2002	11.8
2003	11.9
2004	12
2005	12.1
2006	12.1
2007	12.2
2008	12.3
2009	12.4