Year	Years
1970	1.8
1971	1.9
1972	1.9
1973	2
1974	2.1
1975	2.2
1976	2.2
1977	2.3
1978	2.4
1979	2.5
1980	2.6
1981	2.7
1982	2.7
1983	2.8
1984	2.9
1985	3
1986	3.1
1987	3.2
1988	3.3
1989	3.4
1990	3.5
1991	3.6
1992	3.7
1993	3.9
1994	4
1995	4.1
1996	4.2
1997	4.3
1998	4.4
1999	4.5
2000	4.6
2001	4.8
2002	4.9
2003	5
2004	5.1
2005	5.2
2006	5.4
2007	5.5
2008	5.6
2009	5.7