Year	Years
1970	0.6
1971	0.6
1972	0.7
1973	0.7
1974	0.7
1975	0.8
1976	0.8
1977	0.9
1978	0.9
1979	1
1980	1
1981	1.1
1982	1.2
1983	1.2
1984	1.3
1985	1.4
1986	1.5
1987	1.6
1988	1.7
1989	1.8
1990	1.9
1991	1.9
1992	2
1993	2.1
1994	2.3
1995	2.4
1996	2.5
1997	2.6
1998	2.7
1999	2.8
2000	2.9
2001	3.1
2002	3.2
2003	3.3
2004	3.5
2005	3.6
2006	3.8
2007	3.9
2008	4.1
2009	4.2