Year	Years
1970	6.8
1971	7
1972	7.2
1973	7.4
1974	7.5
1975	7.7
1976	7.9
1977	8
1978	8.2
1979	8.4
1980	8.5
1981	8.7
1982	8.8
1983	9
1984	9.2
1985	9.3
1986	9.5
1987	9.6
1988	9.7
1989	9.9
1990	10
1991	10.1
1992	10.3
1993	10.4
1994	10.5
1995	10.7
1996	10.8
1997	10.9
1998	11
1999	11.1
2000	11.3
2001	11.4
2002	11.5
2003	11.6
2004	11.7
2005	11.8
2006	11.9
2007	12
2008	12.1
2009	12.2