Year	Years
1970	3
1971	3.1
1972	3.2
1973	3.3
1974	3.4
1975	3.5
1976	3.6
1977	3.7
1978	3.8
1979	3.9
1980	4
1981	4.1
1982	4.2
1983	4.3
1984	4.4
1985	4.5
1986	4.6
1987	4.7
1988	4.8
1989	4.9
1990	5
1991	5.1
1992	5.2
1993	5.3
1994	5.4
1995	5.5
1996	5.6
1997	5.7
1998	5.8
1999	5.9
2000	6
2001	6.1
2002	6.2
2003	6.3
2004	6.4
2005	6.5
2006	6.6
2007	6.7
2008	6.8
2009	6.9