Year	Years
1970	1.2
1971	1.3
1972	1.3
1973	1.4
1974	1.5
1975	1.5
1976	1.6
1977	1.6
1978	1.7
1979	1.8
1980	1.8
1981	1.9
1982	2
1983	2
1984	2.1
1985	2.2
1986	2.3
1987	2.3
1988	2.4
1989	2.5
1990	2.6
1991	2.6
1992	2.7
1993	2.8
1994	2.9
1995	2.9
1996	3
1997	3.1
1998	3.2
1999	3.3
2000	3.4
2001	3.4
2002	3.5
2003	3.6
2004	3.7
2005	3.8
2006	3.9
2007	3.9
2008	4
2009	4.1