Year	Years
1970	6.1
1971	6.3
1972	6.6
1973	6.9
1974	7.2
1975	7.4
1976	7.7
1977	8
1978	8.2
1979	8.5
1980	8.7
1981	9
1982	9.2
1983	9.5
1984	9.7
1985	9.9
1986	10.1
1987	10.3
1988	10.5
1989	10.7
1990	10.9
1991	11.1
1992	11.2
1993	11.4
1994	11.6
1995	11.7
1996	11.9
1997	12.1
1998	12.2
1999	12.4
2000	12.5
2001	12.7
2002	12.8
2003	12.9
2004	13
2005	13.2
2006	13.3
2007	13.4
2008	13.5
2009	13.6