Year	Years
1970	9.6
1971	9.7
1972	9.9
1973	10.1
1974	10.3
1975	10.4
1976	10.6
1977	10.8
1978	10.9
1979	11.1
1980	11.2
1981	11.3
1982	11.5
1983	11.6
1984	11.7
1985	11.8
1986	11.9
1987	12
1988	12.1
1989	12.2
1990	12.3
1991	12.4
1992	12.5
1993	12.5
1994	12.6
1995	12.7
1996	12.7
1997	12.8
1998	12.9
1999	12.9
2000	13
2001	13.1
2002	13.1
2003	13.2
2004	13.2
2005	13.3
2006	13.3
2007	13.4
2008	13.4
2009	13.5