Year	Years
1970	0.9
1971	0.9
1972	0.9
1973	1
1974	1
1975	1.1
1976	1.1
1977	1.2
1978	1.2
1979	1.3
1980	1.3
1981	1.4
1982	1.4
1983	1.5
1984	1.6
1985	1.6
1986	1.7
1987	1.8
1988	1.9
1989	1.9
1990	2
1991	2.1
1992	2.2
1993	2.3
1994	2.4
1995	2.4
1996	2.5
1997	2.6
1998	2.7
1999	2.8
2000	2.9
2001	3
2002	3.1
2003	3.2
2004	3.3
2005	3.4
2006	3.6
2007	3.7
2008	3.8
2009	3.9