Year	Years
1970	2.9
1971	3
1972	3.1
1973	3.2
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	4.6
1986	4.7
1987	4.8
1988	4.9
1989	5
1990	5.1
1991	5.2
1992	5.3
1993	5.4
1994	5.5
1995	5.6
1996	5.7
1997	5.8
1998	5.9
1999	6
2000	6.1
2001	6.3
2002	6.4
2003	6.5
2004	6.6
2005	6.7
2006	6.8
2007	6.9
2008	7.1
2009	7.2