Year	Years
1970	4.8
1971	4.9
1972	5.1
1973	5.2
1974	5.3
1975	5.4
1976	5.5
1977	5.7
1978	5.8
1979	5.9
1980	6
1981	6.1
1982	6.3
1983	6.4
1984	6.5
1985	6.6
1986	6.7
1987	6.9
1988	7
1989	7.1
1990	7.2
1991	7.3
1992	7.4
1993	7.6
1994	7.7
1995	7.8
1996	7.9
1997	8
1998	8.1
1999	8.3
2000	8.4
2001	8.5
2002	8.6
2003	8.7
2004	8.8
2005	8.9
2006	9
2007	9.1
2008	9.2
2009	9.3