Year	Years
1970	4.9
1971	5
1972	5.2
1973	5.3
1974	5.5
1975	5.6
1976	5.7
1977	5.9
1978	6
1979	6.2
1980	6.3
1981	6.5
1982	6.6
1983	6.8
1984	6.9
1985	7
1986	7.2
1987	7.3
1988	7.4
1989	7.6
1990	7.7
1991	7.8
1992	8
1993	8.1
1994	8.2
1995	8.3
1996	8.5
1997	8.6
1998	8.7
1999	8.8
2000	8.9
2001	9.1
2002	9.2
2003	9.3
2004	9.4
2005	9.5
2006	9.6
2007	9.7
2008	9.8
2009	9.9