Year	Years
1970	1.1
1971	1.1
1972	1.2
1973	1.3
1974	1.3
1975	1.4
1976	1.5
1977	1.6
1978	1.7
1979	1.7
1980	1.8
1981	1.9
1982	2
1983	2.1
1984	2.2
1985	2.3
1986	2.4
1987	2.6
1988	2.7
1989	2.8
1990	2.9
1991	3.1
1992	3.2
1993	3.3
1994	3.5
1995	3.6
1996	3.8
1997	3.9
1998	4.1
1999	4.2
2000	4.4
2001	4.5
2002	4.7
2003	4.9
2004	5.1
2005	5.3
2006	5.4
2007	5.6
2008	5.8
2009	6