Year	Years
1970	4.2
1971	4.4
1972	4.5
1973	4.6
1974	4.8
1975	4.9
1976	5
1977	5.2
1978	5.3
1979	5.5
1980	5.6
1981	5.7
1982	5.9
1983	6
1984	6.2
1985	6.3
1986	6.5
1987	6.7
1988	6.8
1989	7
1990	7.1
1991	7.3
1992	7.4
1993	7.6
1994	7.8
1995	7.9
1996	8.1
1997	8.2
1998	8.4
1999	8.5
2000	8.7
2001	8.8
2002	9
2003	9.2
2004	9.3
2005	9.5
2006	9.6
2007	9.8
2008	9.9
2009	10