Year	Years
1970	2
1971	2
1972	2.1
1973	2.1
1974	2.2
1975	2.2
1976	2.3
1977	2.3
1978	2.4
1979	2.4
1980	2.4
1981	2.5
1982	2.5
1983	2.5
1984	2.6
1985	2.6
1986	2.6
1987	2.6
1988	2.7
1989	2.7
1990	2.7
1991	2.7
1992	2.8
1993	2.8
1994	2.8
1995	2.9
1996	2.9
1997	2.9
1998	3
1999	3
2000	3
2001	3.1
2002	3.1
2003	3.2
2004	3.2
2005	3.2
2006	3.3
2007	3.3
2008	3.4
2009	3.4