Year	Years
1970	4.5
1971	4.6
1972	4.7
1973	4.9
1974	5
1975	5.2
1976	5.3
1977	5.5
1978	5.6
1979	5.8
1980	5.9
1981	6
1982	6.2
1983	6.3
1984	6.5
1985	6.6
1986	6.8
1987	6.9
1988	7
1989	7.2
1990	7.3
1991	7.5
1992	7.6
1993	7.7
1994	7.9
1995	8
1996	8.1
1997	8.3
1998	8.4
1999	8.5
2000	8.6
2001	8.8
2002	8.9
2003	9
2004	9.1
2005	9.2
2006	9.4
2007	9.5
2008	9.6
2009	9.7