Year	Years
1970	5.2
1971	5.3
1972	5.4
1973	5.5
1974	5.7
1975	5.8
1976	5.9
1977	6
1978	6.2
1979	6.3
1980	6.4
1981	6.5
1982	6.6
1983	6.7
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	7.9
1994	8
1995	8.1
1996	8.2
1997	8.3
1998	8.4
1999	8.5
2000	8.6
2001	8.7
2002	8.8
2003	8.9
2004	9
2005	9.1
2006	9.2
2007	9.3
2008	9.4
2009	9.5