Year	Years
1970	9
1971	9.2
1972	9.3
1973	9.5
1974	9.6
1975	9.8
1976	9.9
1977	10
1978	10.2
1979	10.3
1980	10.4
1981	10.6
1982	10.7
1983	10.8
1984	10.9
1985	11
1986	11.1
1987	11.2
1988	11.3
1989	11.4
1990	11.5
1991	11.6
1992	11.7
1993	11.8
1994	11.8
1995	11.9
1996	12
1997	12.1
1998	12.1
1999	12.2
2000	12.3
2001	12.4
2002	12.4
2003	12.5
2004	12.6
2005	12.6
2006	12.7
2007	12.7
2008	12.8
2009	12.8