Year	Years
1970	5.5
1971	5.6
1972	5.7
1973	5.9
1974	6
1975	6.1
1976	6.2
1977	6.3
1978	6.5
1979	6.6
1980	6.7
1981	6.8
1982	7
1983	7.1
1984	7.2
1985	7.3
1986	7.4
1987	7.6
1988	7.7
1989	7.8
1990	7.9
1991	8
1992	8.1
1993	8.3
1994	8.4
1995	8.5
1996	8.6
1997	8.7
1998	8.8
1999	9
2000	9.1
2001	9.2
2002	9.3
2003	9.4
2004	9.5
2005	9.6
2006	9.8
2007	9.9
2008	10
2009	10.1