Year	Years
1970	11
1971	11.1
1972	11.2
1973	11.3
1974	11.4
1975	11.5
1976	11.6
1977	11.7
1978	11.8
1979	11.9
1980	11.9
1981	12
1982	12.1
1983	12.2
1984	12.3
1985	12.3
1986	12.4
1987	12.5
1988	12.5
1989	12.6
1990	12.7
1991	12.7
1992	12.8
1993	12.9
1994	12.9
1995	13
1996	13
1997	13.1
1998	13.1
1999	13.2
2000	13.3
2001	13.3
2002	13.4
2003	13.4
2004	13.4
2005	13.5
2006	13.5
2007	13.6
2008	13.6
2009	13.7