Year	Years
1970	0.9
1971	1
1972	1.1
1973	1.1
1974	1.2
1975	1.3
1976	1.4
1977	1.4
1978	1.5
1979	1.6
1980	1.7
1981	1.8
1982	1.9
1983	2
1984	2.1
1985	2.2
1986	2.3
1987	2.4
1988	2.5
1989	2.6
1990	2.7
1991	2.8
1992	2.9
1993	3.1
1994	3.2
1995	3.3
1996	3.4
1997	3.6
1998	3.7
1999	3.9
2000	4
2001	4.1
2002	4.3
2003	4.4
2004	4.6
2005	4.7
2006	4.9
2007	5
2008	5.2
2009	5.3