Year	Years
1970	5.7
1971	5.8
1972	6
1973	6.1
1974	6.2
1975	6.3
1976	6.5
1977	6.6
1978	6.7
1979	6.8
1980	7
1981	7.1
1982	7.2
1983	7.3
1984	7.4
1985	7.6
1986	7.7
1987	7.8
1988	8
1989	8.1
1990	8.2
1991	8.3
1992	8.5
1993	8.6
1994	8.7
1995	8.8
1996	9
1997	9.1
1998	9.2
1999	9.3
2000	9.4
2001	9.6
2002	9.7
2003	9.8
2004	9.9
2005	10
2006	10.1
2007	10.3
2008	10.4
2009	10.5