Year	Years
1970	2
1971	2.1
1972	2.2
1973	2.3
1974	2.4
1975	2.4
1976	2.5
1977	2.6
1978	2.7
1979	2.8
1980	2.9
1981	3
1982	3
1983	3.1
1984	3.2
1985	3.3
1986	3.4
1987	3.5
1988	3.6
1989	3.7
1990	3.8
1991	3.9
1992	4
1993	4.1
1994	4.2
1995	4.3
1996	4.4
1997	4.5
1998	4.6
1999	4.7
2000	4.8
2001	5
2002	5.1
2003	5.2
2004	5.3
2005	5.4
2006	5.5
2007	5.7
2008	5.8
2009	5.9