Year	Years
1970	5.1
1971	5.3
1972	5.4
1973	5.5
1974	5.6
1975	5.8
1976	5.9
1977	6
1978	6.2
1979	6.3
1980	6.4
1981	6.5
1982	6.6
1983	6.8
1984	6.9
1985	7
1986	7.1
1987	7.2
1988	7.3
1989	7.4
1990	7.5
1991	7.6
1992	7.7
1993	7.8
1994	7.9
1995	8
1996	8.1
1997	8.2
1998	8.3
1999	8.4
2000	8.5
2001	8.6
2002	8.7
2003	8.8
2004	8.9
2005	9
2006	9
2007	9.1
2008	9.2
2009	9.3