Year	Years
1970	5.1
1971	5.2
1972	5.3
1973	5.5
1974	5.6
1975	5.7
1976	5.9
1977	6
1978	6.1
1979	6.3
1980	6.4
1981	6.5
1982	6.7
1983	6.8
1984	6.9
1985	7.1
1986	7.2
1987	7.3
1988	7.5
1989	7.6
1990	7.8
1991	7.9
1992	8
1993	8.2
1994	8.3
1995	8.4
1996	8.6
1997	8.7
1998	8.8
1999	9
2000	9.1
2001	9.2
2002	9.4
2003	9.5
2004	9.6
2005	9.8
2006	9.9
2007	10
2008	10.1
2009	10.2