Year	Years
1970	2.2
1971	2.2
1972	2.3
1973	2.4
1974	2.5
1975	2.6
1976	2.6
1977	2.7
1978	2.8
1979	2.9
1980	3
1981	3.1
1982	3.2
1983	3.3
1984	3.4
1985	3.5
1986	3.5
1987	3.6
1988	3.7
1989	3.8
1990	3.9
1991	4
1992	4.1
1993	4.2
1994	4.3
1995	4.4
1996	4.6
1997	4.7
1998	4.8
1999	4.9
2000	5
2001	5.1
2002	5.2
2003	5.3
2004	5.4
2005	5.5
2006	5.6
2007	5.7
2008	5.8
2009	5.9