Year	Years
1970	5.6
1971	5.8
1972	5.9
1973	6.1
1974	6.2
1975	6.3
1976	6.5
1977	6.6
1978	6.7
1979	6.9
1980	7
1981	7.1
1982	7.3
1983	7.4
1984	7.6
1985	7.7
1986	7.8
1987	8
1988	8.1
1989	8.2
1990	8.3
1991	8.5
1992	8.6
1993	8.7
1994	8.8
1995	9
1996	9.1
1997	9.2
1998	9.3
1999	9.4
2000	9.6
2001	9.7
2002	9.8
2003	9.9
2004	10
2005	10.1
2006	10.2
2007	10.3
2008	10.4
2009	10.5