Year	Years
1970	0.6
1971	0.6
1972	0.6
1973	0.7
1974	0.7
1975	0.8
1976	0.8
1977	0.8
1978	0.9
1979	0.9
1980	1
1981	1
1982	1.1
1983	1.2
1984	1.2
1985	1.3
1986	1.3
1987	1.4
1988	1.4
1989	1.5
1990	1.6
1991	1.6
1992	1.7
1993	1.8
1994	1.8
1995	1.9
1996	2
1997	2.1
1998	2.2
1999	2.3
2000	2.4
2001	2.4
2002	2.5
2003	2.6
2004	2.7
2005	2.8
2006	3
2007	3.1
2008	3.2
2009	3.3