Year	Years
1970	1.3
1971	1.3
1972	1.4
1973	1.4
1974	1.5
1975	1.6
1976	1.6
1977	1.7
1978	1.8
1979	1.9
1980	1.9
1981	2
1982	2.1
1983	2.2
1984	2.3
1985	2.4
1986	2.4
1987	2.5
1988	2.6
1989	2.7
1990	2.8
1991	2.9
1992	3
1993	3.1
1994	3.1
1995	3.2
1996	3.3
1997	3.4
1998	3.5
1999	3.6
2000	3.7
2001	3.8
2002	3.9
2003	4
2004	4.1
2005	4.2
2006	4.3
2007	4.4
2008	4.5
2009	4.6