Year	Years
1970	2.9
1971	3.1
1972	3.2
1973	3.3
1974	3.4
1975	3.6
1976	3.7
1977	3.8
1978	4
1979	4.1
1980	4.2
1981	4.4
1982	4.5
1983	4.7
1984	4.8
1985	4.9
1986	5.1
1987	5.2
1988	5.4
1989	5.5
1990	5.6
1991	5.8
1992	5.9
1993	6.1
1994	6.2
1995	6.3
1996	6.5
1997	6.6
1998	6.8
1999	6.9
2000	7.1
2001	7.2
2002	7.3
2003	7.5
2004	7.6
2005	7.8
2006	7.9
2007	8
2008	8.2
2009	8.3