Year	Years
1970	5.6
1971	5.8
1972	5.9
1973	6.1
1974	6.2
1975	6.4
1976	6.6
1977	6.7
1978	6.8
1979	7
1980	7.1
1981	7.3
1982	7.4
1983	7.6
1984	7.7
1985	7.9
1986	8
1987	8.1
1988	8.3
1989	8.4
1990	8.5
1991	8.6
1992	8.8
1993	8.9
1994	9
1995	9.1
1996	9.3
1997	9.4
1998	9.5
1999	9.6
2000	9.8
2001	9.9
2002	10
2003	10.1
2004	10.2
2005	10.3
2006	10.4
2007	10.5
2008	10.6
2009	10.8