Year	Years
1970	5.6
1971	5.7
1972	5.9
1973	6
1974	6.2
1975	6.3
1976	6.5
1977	6.6
1978	6.7
1979	6.9
1980	7
1981	7.2
1982	7.3
1983	7.5
1984	7.6
1985	7.8
1986	7.9
1987	8.1
1988	8.2
1989	8.3
1990	8.5
1991	8.6
1992	8.7
1993	8.9
1994	9
1995	9.1
1996	9.3
1997	9.4
1998	9.5
1999	9.7
2000	9.8
2001	9.9
2002	10
2003	10.1
2004	10.3
2005	10.4
2006	10.5
2007	10.6
2008	10.7
2009	10.8