Year	Years
1970	4.4
1971	4.6
1972	4.7
1973	4.8
1974	5
1975	5.1
1976	5.2
1977	5.3
1978	5.5
1979	5.6
1980	5.7
1981	5.9
1982	6
1983	6.1
1984	6.2
1985	6.4
1986	6.5
1987	6.6
1988	6.7
1989	6.9
1990	7
1991	7.1
1992	7.2
1993	7.4
1994	7.5
1995	7.6
1996	7.7
1997	7.8
1998	8
1999	8.1
2000	8.2
2001	8.3
2002	8.4
2003	8.5
2004	8.7
2005	8.8
2006	8.9
2007	9
2008	9.1
2009	9.2