Year	Years
1970	4.7
1971	4.9
1972	5
1973	5.1
1974	5.2
1975	5.4
1976	5.5
1977	5.6
1978	5.8
1979	5.9
1980	6
1981	6.1
1982	6.3
1983	6.4
1984	6.6
1985	6.7
1986	6.9
1987	7
1988	7.2
1989	7.3
1990	7.5
1991	7.6
1992	7.7
1993	7.9
1994	8
1995	8.2
1996	8.3
1997	8.4
1998	8.6
1999	8.7
2000	8.8
2001	8.9
2002	9.1
2003	9.2
2004	9.3
2005	9.4
2006	9.5
2007	9.7
2008	9.8
2009	9.9