Year	Years
1970	5.1
1971	5.2
1972	5.3
1973	5.4
1974	5.6
1975	5.7
1976	5.8
1977	5.9
1978	6
1979	6.1
1980	6.3
1981	6.4
1982	6.5
1983	6.6
1984	6.7
1985	6.8
1986	6.9
1987	7
1988	7.1
1989	7.2
1990	7.3
1991	7.4
1992	7.5
1993	7.5
1994	7.6
1995	7.7
1996	7.8
1997	7.9
1998	8
1999	8.1
2000	8.1
2001	8.2
2002	8.3
2003	8.4
2004	8.5
2005	8.5
2006	8.6
2007	8.7
2008	8.8
2009	8.8