Year	Years
1970	2.2
1971	2.3
1972	2.4
1973	2.5
1974	2.6
1975	2.7
1976	2.8
1977	2.9
1978	3
1979	3.1
1980	3.2
1981	3.4
1982	3.5
1983	3.6
1984	3.7
1985	3.8
1986	4
1987	4.1
1988	4.2
1989	4.3
1990	4.4
1991	4.6
1992	4.7
1993	4.8
1994	4.9
1995	5.1
1996	5.2
1997	5.3
1998	5.4
1999	5.6
2000	5.7
2001	5.8
2002	6
2003	6.1
2004	6.2
2005	6.4
2006	6.5
2007	6.6
2008	6.8
2009	6.9