Year	Years
1970	5.6
1971	5.7
1972	5.9
1973	6
1974	6.2
1975	6.4
1976	6.5
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	8.7
1993	8.8
1994	8.9
1995	9
1996	9
1997	9.1
1998	9.2
1999	9.3
2000	9.4
2001	9.4
2002	9.5
2003	9.6
2004	9.7
2005	9.7
2006	9.8
2007	9.8
2008	9.9
2009	9.9