Year	Years
1970	0.9
1971	0.9
1972	1
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	1.5
1983	1.5
1984	1.6
1985	1.7
1986	1.7
1987	1.8
1988	1.9
1989	2
1990	2.1
1991	2.2
1992	2.3
1993	2.4
1994	2.5
1995	2.6
1996	2.7
1997	2.8
1998	2.9
1999	3
2000	3.1
2001	3.2
2002	3.3
2003	3.4
2004	3.5
2005	3.6
2006	3.7
2007	3.9
2008	4
2009	4.1