Year	Years
1970	4.8
1971	4.9
1972	5.1
1973	5.2
1974	5.4
1975	5.5
1976	5.6
1977	5.8
1978	5.9
1979	6.1
1980	6.2
1981	6.4
1982	6.5
1983	6.7
1984	6.8
1985	7
1986	7.1
1987	7.3
1988	7.5
1989	7.6
1990	7.8
1991	7.9
1992	8.1
1993	8.3
1994	8.4
1995	8.6
1996	8.7
1997	8.9
1998	9
1999	9.2
2000	9.3
2001	9.5
2002	9.6
2003	9.7
2004	9.9
2005	10
2006	10.2
2007	10.3
2008	10.4
2009	10.6