Year	Years
1970	11.3
1971	11.4
1972	11.5
1973	11.6
1974	11.7
1975	11.8
1976	11.9
1977	12
1978	12.1
1979	12.1
1980	12.2
1981	12.3
1982	12.4
1983	12.4
1984	12.5
1985	12.6
1986	12.7
1987	12.7
1988	12.8
1989	12.8
1990	12.9
1991	13
1992	13
1993	13.1
1994	13.1
1995	13.2
1996	13.2
1997	13.3
1998	13.3
1999	13.3
2000	13.4
2001	13.4
2002	13.5
2003	13.5
2004	13.6
2005	13.6
2006	13.6
2007	13.7
2008	13.7
2009	13.7