Year	Years
1970	0.9
1971	1
1972	1
1973	1
1974	1.1
1975	1.1
1976	1.2
1977	1.2
1978	1.3
1979	1.3
1980	1.4
1981	1.5
1982	1.5
1983	1.6
1984	1.6
1985	1.7
1986	1.8
1987	1.8
1988	1.9
1989	2
1990	2.1
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	3.2
2005	3.3
2006	3.4
2007	3.5
2008	3.6
2009	3.7