Year	Years
1970	5.3
1971	5.4
1972	5.5
1973	5.6
1974	5.8
1975	5.9
1976	6
1977	6.1
1978	6.3
1979	6.4
1980	6.5
1981	6.7
1982	6.8
1983	6.9
1984	7.1
1985	7.2
1986	7.3
1987	7.5
1988	7.6
1989	7.7
1990	7.9
1991	8
1992	8.1
1993	8.3
1994	8.4
1995	8.5
1996	8.7
1997	8.8
1998	8.9
1999	9
2000	9.2
2001	9.3
2002	9.4
2003	9.5
2004	9.6
2005	9.8
2006	9.9
2007	10
2008	10.1
2009	10.2