Year	Years
1970	0.7
1971	0.8
1972	0.8
1973	0.9
1974	1
1975	1
1976	1.1
1977	1.2
1978	1.2
1979	1.3
1980	1.4
1981	1.5
1982	1.6
1983	1.7
1984	1.8
1985	1.9
1986	2.1
1987	2.2
1988	2.3
1989	2.4
1990	2.5
1991	2.7
1992	2.8
1993	2.9
1994	3
1995	3.2
1996	3.3
1997	3.4
1998	3.6
1999	3.7
2000	3.9
2001	4
2002	4.2
2003	4.3
2004	4.5
2005	4.6
2006	4.8
2007	4.9
2008	5.1
2009	5.3