Year	Years
1970	0.9
1971	0.9
1972	1
1973	1
1974	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	1.7
1985	1.8
1986	1.9
1987	1.9
1988	2
1989	2.1
1990	2.2
1991	2.3
1992	2.4
1993	2.5
1994	2.6
1995	2.7
1996	2.8
1997	2.9
1998	3
1999	3.2
2000	3.3
2001	3.4
2002	3.5
2003	3.7
2004	3.8
2005	3.9
2006	4.1
2007	4.2
2008	4.4
2009	4.5