Year	Years
1970	7.5
1971	7.7
1972	7.8
1973	7.9
1974	8.1
1975	8.2
1976	8.3
1977	8.5
1978	8.6
1979	8.7
1980	8.9
1981	9
1982	9.1
1983	9.3
1984	9.4
1985	9.5
1986	9.7
1987	9.8
1988	9.9
1989	10
1990	10.2
1991	10.3
1992	10.4
1993	10.5
1994	10.6
1995	10.7
1996	10.9
1997	11
1998	11.1
1999	11.2
2000	11.3
2001	11.4
2002	11.5
2003	11.6
2004	11.7
2005	11.8
2006	11.9
2007	11.9
2008	12
2009	12.1